My Arm is Flippin tired...Tec HM80

#1
Something isn't right. I put a new carb on this HM80. It will run if I screw the needles and all the way in but it backfires a bit. If I idle it up it is worse. If I try to back the screw out it starts to die. I think it is running too rich with the needle all the way in. Maybe I got the wrong carb. This carb has a different throttle hook up. And the fuel inlet comes straight out the side instead of a 90 degree elbow down to the fuel pump.

Any advice is Welcome.
 
#2
I'm not very familiar with that engine but the needles aren't suppose to be all the way screwed in. The HS40's are 1 back out and 1 1/2 back out on the screws.
 
#4
check and check, but I think I found the problem. I need to read carb descriptions better. I bought a carb for an h80. not an hm80. I'm guessing that will make a difference. I'm surprised that I've lived this long. I have my head up my butt so much you would have thought I would have suffocated by now. Stupid things I do.
 

george3

Active Member
#5
did you buy a china carb? H80 and HM 80 same but the style of throttle and maybe choke levers should run correctly unless you spent the big bucks on the 5.00 china carb. Them carbs are POS.
 
#6
did you buy a china carb? H80 and HM 80 same but the style of throttle and maybe choke levers should run correctly unless you spent the big bucks on the 5.00 china carb. Them carbs are POS.
Yes. China carb. I took a chance and I ordered the other one last night. Should have not been so tight. That's what you get I guess.
 
#9
I give up. I have no idea what is going on. Usually, given enough time, I can get these things figured out but this one is kicking my butt. It sucks because I have everything I need to finish this bike. I was hoping to finish this weekend. I got a new carb yesterday. Wrong again. This one doesn't have an adjustment screw on the bottom. It will run with it but if you give it throttle it dies. What gives. Two new carbs both did not help at all.

I did check the key way, it is good. Took the head off to see if the valves were closing. I notice one thing. On the way up with the compression stroke , the exhaust valve seems to open a bit and then close before the piston gets about 3/4 of the way up. That is the only thing that looks funny to me. Please, any ideas.
 
#10
Did you check the fuel pump ? You might try using a test tank and let it gravity feed. What's wrong with original carb ?
 
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#13
ok, I took the carb apart again and put it back on. I checked for cracks that air could get through, again. This time I filled the tank all the way up so that the level was above the bowl. It ran better. AND, you are going to be disgusted with me, I was trying all of this with the air filter off. I think that was the kicker. I reread Gumpit's post above about the air cleaner and it dawned on me that maybe that needs to be on there. dumb huh.

Anyway, I am going back out to try to fine tune it..

I wasn't aware that these engines had a compression release. Glad that I didn't tear the case apart. thanks

Any tips for final tuning?
 
#15
I have the engine running but I can't get it to clean up. Run it at fast idle and it cleans up. If I idle it down it dies. If I adjust for idle it runs rough on the top end. I can't get it on both ends. When it is good on the top it will idle if I put it at half choke it will idle. I just see-saw back and forth with it. Any ideas?
 

bikebudy

Banned - Must pay $500
#16
Now, I don't know what carb you have but, this is the one I got. # 151331585729

Said to be for 7, 8, & 9hp engines. Mine is a 7hp , HM70

Turned up the idle, started it, tuned in the high speed an I was set. ( Could be luck, could be all was set just right every other way.)

Fuel pumps seem to cause a lot of over fueling problems.
 
#17
I would have to mount a different fuel tank if I eliminated the pump. I see pictures of SuperBroncs with a separate tank. Are they suppose to have them.
 
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