Clements 28mm carburetor

Mini Bike & Go-Kart Parts

#1
Hi guys so I have a question. I recently replaced my makuni 26mm carb. With a Clements 28mm carb, when I went out to go for some test pulls. There’s no throttle response even at part throttle or full throttle feels like it wants to die/bog. When I had the 26mm carb it ran perfect. Could it be starving for fuel. I currently don’t have a fuel pump hooked up. Any advice would be greatly appreciated
mods:
Big valve head, ported and polish and milled
.310 cam advance to 2 degrees
1.2 gage roller rockers
 
#2
Does it idle ok? When you open it to half throttle does it accelerate ok? If you give it 1/4 throttle is it ok?robably should check float level, needle is installed ok and check main jet size
 
#3
Does it idle ok? When you open it to half throttle does it accelerate ok? If you give it 1/4 throttle is it ok?robably should check float level, needle is installed ok and check main jet size
It idle’s ok. Half throttle it accelerate with somewhat feel like a bad bog doesn’t accelerate. I have to let go of throttle and when I just try to full throttle it it feels like it wants to die and I have to let off the throttle.
 
#4
Your description of half throttle is confusing. Please clarify does it accelerate ok or if it does not what are your symptoms. Does the engine sound funny, is it misfiring or shutting off then on. What color is the spark plug? Does your clements carb have the third jet in the inlet horn connected to the float bowl by a hose like this picture? Is the carb the only change you made? And you did say it ran good with the 26mm Makuni correct?
 

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#5
Your description of half throttle is confusing. Please clarify does it accelerate ok or if it does not what are your symptoms. Does the engine sound funny, is it misfiring or shutting off then on. What color is the spark plug? Does your clements carb have the third jet in the inlet horn connected to the float bowl by a hose like this picture? Is the carb the only change you made? And you did say it ran good with the 26mm Makuni correct?
I’m sorry for the confusion. It does accelerate. The engine does not sound funny, it’s not misfiring. But when I start the bike when it’s cold with choke level pulled and I pull the choke down like 3mins in from starting the bike it wants to shuts off but I give it a little throttle so it won’t die. The spark plug is brown/caramel color. And the third jet in the inlet horn hose is connected like in the picture. Yes the carb is the only thing that I’ve change and yes sir it ran good with the 26mm makuni. Will not enough fuel delivery cause any of the hesitation no power symptom I have by not having a fuel pump and just running my fuel gravity fed. Also I don’t know if the company I bought the carb sent me the alky carb as they make one for gas and alky . And thanks ole for trying to help me
 
#6
If it is a alky carb it would be so rich it would smoke black out the exhaust and the plug would be a dry black color. So lets talk about the 3 miniutes issue, the carb has a idle enrichment circuit not a choke. When you pull up the enrichment plunger it uncovers a hole that lets in more fuel as well as more air. it should be used to start the bike and after it runs for at most 30 seconds you should be able to push it down and it should still run. You have two adjustment to get it to idle correctly the slide height and the air bleed adjustment. I will have to look at mine to verify that on that carb it is in fact a air bleed not a fuel adjustment. On the air bleed adjustments opening it leans it our and on the fuel adjusters opening it richens it up. It sounds like you are lean. You may want to check the float height and also look at what the pilot jet is. The main jet affects mostly the 3/4 to open throttle performance so you should see what number is on that one as well. Here is a link to the Kehin chart, pay attention to the adjustments for a PWK carb as yours are copies of a pwk. slide_valve.pdf (keihin-na.com)
 
#7
Your description of half throttle is confusing. Please clarify does it accelerate ok or if it does not what are your symptoms. Does the engine sound funny, is it misfiring or shutting off then on. What color is the spark plug? Does your clements carb have the third jet in the inlet horn connected to the float bowl by a hose like this picture? Is the carb the only change you made? And you did say it ran good with the 26mm Makuni correct?
I’m sorry for the confusion. It does accelerate. The engine does not sound funny, it’s not misfiring
If it is a alky carb it would be so rich it would smoke black out the exhaust and the plug would be a dry black color. So lets talk about the 3 miniutes issue, the carb has a idle enrichment circuit not a choke. When you pull up the enrichment plunger it uncovers a hole that lets in more fuel as well as more air. it should be used to start the bike and after it runs for at most 30 seconds you should be able to push it down and it should still run. You have two adjustment to get it to idle correctly the slide height and the air bleed adjustment. I will have to look at mine to verify that on that carb it is in fact a air bleed not a fuel adjustment. On the air bleed adjustments opening it leans it our and on the fuel adjusters opening it richens it up. It sounds like you are lean. You may want to check the float height and also look at what the pilot jet is. The main jet affects mostly the 3/4 to open throttle performance so you should see what number is on that one as well. Here is a link to the Kehin chart, pay attention to the adjustments for a PWK carb as yours are copies of a pwk. slide_valve.pdf (keihin-na.com)
ok thanks for verifying the choke is an enrichment plunger. So the air bleed or idle screw is the screw with a spring on it correct? Also my air/fuel screw is on the bottom top right of the horn correct? And turning the air/fuel screw in leans it out and turning it counter clockwise richens it up correct?. When I get home I will take a picture of the pilot jet and main jet. Thanks again
 
#8
the adjuster with the black knob in the picture below adjusts the slide height. The airscrew is the brass screw below the slide height adjuster. This screw is commonly referred to as the "air screw" and it meters the amount of AIR in the idle mixture, therefore turning the SCREW out will lean the mixture and turning the SCREW in (clockwise) will richen the mixture. To adjust it Set the air screw to 1 turn out. Start the motor Set the idle with the idle screw as low as you can NOW, TURN THE AIR SCREW OUT to raise the idle. If the idle goes too high, lower it with the idle screw. In other words, use the air screw to raise the idle as high as you can, then correct it with the idle screw (slide height adjuster) The slide height also affects the idle mixture as raising it allows more air in under the slide, so you would screw in the air screw to richen it up. You may have to go back and forth till you get the idle you want. Once you have that then you can go test it and then if your still having issues we can go adress that. There are 3 steps to adjusting these idle, (slide height, air screw, Pilot jet) Then needle height, (1/4 to 3/4 throttle) then main jet. The extra hi speed fuel jet can complicate the main jet requirements but we will worry about that later.
 

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#9
the adjuster with the black knob in the picture below adjusts the slide height. The airscrew is the brass screw below the slide height adjuster. This screw is commonly referred to as the "air screw" and it meters the amount of AIR in the idle mixture, therefore turning the SCREW out will lean the mixture and turning the SCREW in (clockwise) will richen the mixture. To adjust it Set the air screw to 1 turn out. Start the motor Set the idle with the idle screw as low as you can NOW, TURN THE AIR SCREW OUT to raise the idle. If the idle goes too high, lower it with the idle screw. In other words, use the air screw to raise the idle as high as you can, then correct it with the idle screw (slide height adjuster) The slide height also affects the idle mixture as raising it allows more air in under the slide, so you would screw in the air screw to richen it up. You may have to go back and forth till you get the idle you want. Once you have that then you can go test it and then if your still having issues we can go adress that. There are 3 steps to adjusting these idle, (slide height, air screw, Pilot jet) Then needle height, (1/4 to 3/4 throttle) then main jet. The extra hi speed fuel jet can complicate the main jet requirements but we will worry about that later.
Okay I will try and set the idle tomorrow. Also do I set the air screw all the way in and back it out 1 turn and than start the bike and start adjusting?, also here’s a picture of the spark plug 938D6DF7-88F1-4600-9731-384B68310B4A.jpeg
 
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#10
The plug looks to me like it is lean but not sure why I see orange. If it was too rich it would be a lot darker. ! turn out is a good starting point, then start let it warm up on enrichner then turn off enrichner and see if it idles, if it does then try going in and out to get the highest rpm. If it ill not run then raise the slide about a 1/8 to 1/4 turn and try again to see if you can get it to idle. Don't forget that you have the working 26mm carb to compare to so you can see what jets are in that one and compare float heights as well. The main jet on the 28 should be a small bit bigger than the 26mm carb.
 
#11
The plug looks to me like it is lean but not sure why I see orange. If it was too rich it would be a lot darker. ! turn out is a good starting point, then start let it warm up on enrichner then turn off enrichner and see if it idles, if it does then try going in and out to get the highest rpm. If it ill not run then raise the slide about a 1/8 to 1/4 turn and try again to see if you can get it to idle. Don't forget that you have the working 26mm carb to compare to so you can see what jets are in that one and compare float heights as well. The main jet on the 28 should be a small bit bigger than the 26mm carb.
Ok sounds good. Also I forgot to mention that I’m running race gas at the moment, i don’t know if that make a difference in spark plug coloration.
 
#12
The plug looks to me like it is lean but not sure why I see orange. If it was too rich it would be a lot darker. ! turn out is a good starting point, then start let it warm up on enrichner then turn off enrichner and see if it idles, if it does then try going in and out to get the highest rpm. If it ill not run then raise the slide about a 1/8 to 1/4 turn and try again to see if you can get it to idle. Don't forget that you have the working 26mm carb to compare to so you can see what jets are in that one and compare float heights as well. The main jet on the 28 should be a small bit bigger than the 26mm carb.
So I did what you told me to do. As far as get the bike started and have it idle and adjust the air screw etc. but the farthest I got the idle to settle was around 2460RPM. Tried to ride it around and still feels like it want to die at half throttle. Turned off bike and checked spark plug found spark plug running rich. Then tried starting bike again but now it’s hard to start it. And also have a pull back now, I’ve always have a little starting it because I have no decompression spring on my billet cam. But the pull back is more noticeable.
 
#13
can you please list all the modifications to your engine it would help. Include valve sizes, cam lift and duration. On my motors without a compression relief they can only be started with the electric coleman starter and even that has a hard time. It will yank the pull starter out of my hand every time. So lets go back to the idle, unless you have a air leak 2460 is a bit too high and would probably start to engage your clutch unless you set the engagement rpm at 3000 rpm. If your plug is real black it may be gas fouled so get yourself some cheap plugs as you may go thru a few getting this carb dialed in. So just to be clear it is now idling at 2460 rpm with the enrichner off (the plastic knob pushed down correct? If you remove the air cleaner check the open space under the slide using small drill sizes till you find one that just fits under the slide without moving it and tell us the dimension. Normally with a carb like that you adjust the idle air screw to the fastest rpm, then adjust the slide height to get to the rpm you want, then re adjust the air screw for fastest rpm and then turn in 1/8 turn to ever so slightly richen it. You may have to do that a number of times. If you check slide height and it is all the way down and it still idles fast you have a air leak somewhere or the enrichner plunger is not seating. I am amazed you are able to pull start it with no compression release, Your a better man than me, I have a hard time pull starting my 6:1 tecumseh with a non compression release cam. I have to remember to pull it past compression before pulling. My bikes sit for long periods of time and when I go to start that Tecumseh I usually forget about the starting ritual and give it a yank and get the cord yanked out of my hand.
 
#14
can you please list all the modifications to your engine it would help. Include valve sizes, cam lift and duration. On my motors without a compression relief they can only be started with the electric coleman starter and even that has a hard time. It will yank the pull starter out of my hand every time. So lets go back to the idle, unless you have a air leak 2460 is a bit too high and would probably start to engage your clutch unless you set the engagement rpm at 3000 rpm. If your plug is real black it may be gas fouled so get yourself some cheap plugs as you may go thru a few getting this carb dialed in. So just to be clear it is now idling at 2460 rpm with the enrichner off (the plastic knob pushed down correct? If you remove the air cleaner check the open space under the slide using small drill sizes till you find one that just fits under the slide without moving it and tell us the dimension. Normally with a carb like that you adjust the idle air screw to the fastest rpm, then adjust the slide height to get to the rpm you want, then re adjust the air screw for fastest rpm and then turn in 1/8 turn to ever so slightly richen it. You may have to do that a number of times. If you check slide height and it is all the way down and it still idles fast you have a air leak somewhere or the enrichner plunger is not seating. I am amazed you are able to pull start it with no compression release, Your a better man than me, I have a hard time pull starting my 6:1 tecumseh with a non compression release cam. I have to remember to pull it past compression before pulling. My bikes sit for long periods of time and when I go to start that Tecumseh I usually forget about the starting ritual and give it a yank and get the cord yanked out of my hand.
Trust me I’ve learned my lesson of just pull starting it. I have a electric start on it but yet sometimes electric start sometimes won’t start it so I have to use electric start and pull start it.
MODS:
70mm flat top piston
Racing head 32/28 ported and milled to 0.065”
Dyno cam adjustable .310 cam advance to 2degree paired with 1.2 gage roller rockers
Dual titanium valve springs
ARC 6254 Rod
ARC Billet electric start flywheel
The flat slide is all the way down and yet still Revving high. Yeah my clutch engages so I have the bike on a block to keep it from going. Yes the bike revs to 2460 with plunger down. When I looked at the plug it wasn’t very black but it was a black color of it knowing it’s running rich. I’m kind of stump right now. Never had this kind of issue with a flatslide
 
#15
OK so if the slide is all the way down there is an air leak somewhere. If this was not an issue with the 26mm carb and you just replaced the carb but left manifold untouched we can make an assumption that either there is a leak where the spigot of the carb enters the boot, or if you removed the boot where the spigot mount o-ring meets the manifold. I am posting pics of the slide adjusted correctly and another which is all the way down and not letting in any air, please verify that yours is closed like the picture by removing carb and looking at the backside. If it is closed all the way like the second picture then for sure that carb is leaking air otherwise the motor would not run. If you look at the hole on the side about 1/2 inch in the bore on the spigot side you should see the brass plunger covering it. If it is not all the way down then that is your air leak. Dissasemble the enricher and see why it is not seating. The hole at the bottom is the air fuel from the air screw adjustment and pilot jet. Now I have no idea what Clements did to that carb if anything but if I sight down that hole there is a brass jet with a tiny hole in it, make sure you have that in yours. I was going to ask why you thought you needed a 28mm carb in the first place but with your engine mods it is appropriate.
 

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#16
OK so if the slide is all the way down there is an air leak somewhere. If this was not an issue with the 26mm carb and you just replaced the carb but left manifold untouched we can make an assumption that either there is a leak where the spigot of the carb enters the boot, or if you removed the boot where the spigot mount o-ring meets the manifold. I am posting pics of the slide adjusted correctly and another which is all the way down and not letting in any air, please verify that yours is closed like the picture by removing carb and looking at the backside. If it is closed all the way like the second picture then for sure that carb is leaking air otherwise the motor would not run. If you look at the hole on the side about 1/2 inch in the bore on the spigot side you should see the brass plunger covering it. If it is not all the way down then that is your air leak. Dissasemble the enricher and see why it is not seating. The hole at the bottom is the air fuel from the air screw adjustment and pilot jet. Now I have no idea what Clements did to that carb if anything but if I sight down that hole there is a brass jet with a tiny hole in it, make sure you have that in yours. I was going to ask why you thought you needed a 28mm carb in the first place but with your engine mods it is appropriate.
I was thinking of running methanol the reason for the 28mm carb change. Also can or will where the cable run through on top doesn't have a boot cause air leak also? I also checked the back of the slide and it was like the third picture its not fully closed. ok so when I press down on the plugger since there's gas everytime I press it down with the plunger down putting pressure on it I can see bubbles.
 
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#17
The third picture is closed, 4th picture is slightly open. The top boot missing will let a bit of a leak but will not really affect it. So please clarify is your slide all the way down like pic 3 or open like the 4th picture. As long as plunger goes all the way down and the rubber sealing washer on the bottom of the plunger is ok then it's not you problem.
 
#18
The third picture is closed, 4th picture is slightly open. The top boot missing will let a bit of a leak but will not really affect it. So please clarify is your slide all the way down like pic 3 or open like the 4th picture. As long as plunger goes all the way down and the rubber sealing washer on the bottom of the plunger is ok then it's not you problem.
Sorry! Wasn’t paying attention, it’s the 4th picture. Also can you clarify to me, so my billet flywheel is 32BTDC and I added a 4 degree timing key. Do I also advance my cam to 4 degree also? I’m so sorry for asking all this question. I’m somewhat kind of new to this small engine building stuff and carb setup. I really appreciate you taking your time helping me and trying to figure out my issues.
 
#19
For gas you should run 32 degrees. I've heard people add a couple of degrees for meth but I have no experience running alcohol. So try to see if you can lower slide with the slide adjuster if it does not close the throttle cable may be holding open.
 
#20
For gas you should run 32 degrees. I've heard people add a couple of degrees for meth but I have no experience running alcohol. So try to see if you can lower slide with the slide adjuster if it does not close the throttle cable may be holding open.
I tried adjusting the slide with the slide adjuster and got it to close a little, the slide is still slightly open I would say like a mm open. I’m also thinking it could be the throttle cable holding it open. Is there any other solution on the throttle cable
 

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