New build, straight line speed attempt...

I74

I74

Well-Known Member
#61
#61
That sucks ! :confused:
I would try some kind of hefty isolation grommet next time, like what the ones for the oil tanks on old Harleys ect. looked like , but ''way'' more solid.
Seems like I remember from many years back,, that some of the Semi tractors ect. had real hefty threaded rubber mounting grommets around the engine compartments for mounting stuff....
They make them, ''or did'',, with one end threaded male , & the other end female.
If it were me, - ''starting fresh of course'' ,, I would put a threaded stud in the head first, & then the female threaded end.
Think that would help ''a lot'' in keeping things intact better. ;)
I
 
I74

I74

Well-Known Member
#62
#62
Added,,
thinking more of this, especially with the long pipe,,
I would definitely add an additional bracket tied in somewhere else.
That head casting has hardly any support for that by itself, regardless.
 
noseoil

noseoil

Active Member
#64
#64
Got the new head & did the porting. What a pleasure it is to use the Makita die grinder compared to last time. It's a bit more aggressive with new carbide burrs, but it made short work of the cutting. I was a bit more aggressive this time on the guides (what guides!) & opened things up more for higher rpms. It's much better than last time. Went back in with a dremel & smoothed things out with a small sanding drum & smaller burrs, so the head's good now.

Got it put back together this morning & it's running. I changed back to a higher gear ratio to take advantage of the higher rpms with the Black Mamba cam, but it's still not pulling much over 7400 rpm. I went for a short ride & it still feels "starved" at 7400 rpm, so I need to look at jetting & the air up here. Here's a link to a better explanation of what I did with the header & bracket to make things right.
https://www.mbd-minibikedrags.org/forum/times-speeds-hp/speeds-on-the-red-bike
 
I74

I74

Well-Known Member
#65
#65
Went to your site.
Had problems posting there.
My ''Old School'' recommendation on the carb is : Champher the jets.
Use a drill bit, & radious the holes, down to the size that they are.
Basically, use a larger bit than the holes are, & taper the inlet to the size of the hole.
I would then smooth the hole out lightly with a Dremel, or something.
That will then make the inlet of the hole tapered, & help with more inlet flow.;)

I
 
I74

I74

Well-Known Member
#66
#66
Added,,
The emulsion tube is a progression tube above the main jet, that pretty much regulates fuel from idle to full on.
There is usually multiple holes in that tube.
You need to figure where the flat spots ect. are,, between idle & full on,, & Champher holes in the emulsion tube, where you think a flat spot is.
That usually helps in smoothing out from between idle & full on.
I would use smaller dill bits ect. first, & go from there.

Ian
 
noseoil

noseoil

Active Member
#67
#67
Web site is a PITA. You would need to join (your email becomes your user name) then you might be able to post, or maybe not. It's a nasty software which needs more time than I've devoted to it for now. Best of luck if you try.

As it stands now, the only spot I'm having trouble with is at WOT on a longer pull, where it can build more revs & push more air out of the way. It's acting like a "starved" issue, the best way I can describe it to you. Up to that point it pulls very well. I'm wondering if it isn't just a question of air density as a function of horse power. At 1600' elevation it would scream to 8400 rpm & I would back out of it. With 6500' (3% loss of hp per 1000' elevation gain) that's about 15% less hp, so perhaps I'm just beating a dead horse by trying to run faster up here. I'll keep working on it & post what I find.
 
I74

I74

Well-Known Member
#68
#68
I lived up in the mountains around Colorado for years.
Am definitely thinking that you need more air, & the timing advanced for the higher altitudes.
I used to scribe 2 degree ''advance'' increment marks on timing plates of Harley's, & at the base of distributors on cars ect.
Pretty much ran 1 degree more advance for every 2k ft. of elevation.

If you have multiple key slots on the flywheel, I would try the advanced slot, for that altitude, & take the cover off the air filter,, if you haven't yet.

An offset key for advance, would help also,, if you don't have extra slots.;)
 
I74

I74

Well-Known Member
#69
#69
Added,,
Another trick is to long gate the mounting holes on the coil pack, & move/ advance it closer to the rotation.
You might gain a couple of degrees or so advance in just doing that.
 
noseoil

noseoil

Active Member
#70
#70
With the ARC flywheel it's already running a 32 degree advance. I don't have a wheel, so that's based on their specs & is a pretty good guess about the timing.

Thinking I may pull the air filter for a pass or two, just to see if it's not breathing as well as it can up here. Next step/question would be the valves as this may be the "weak point" in airflow through the engine. I might just be maxed out with things & air flow isn't up to the task of making more ponies up here with the thin air. Starting to feel like the mythical "Whiffle Bird" of old...
 
noseoil

noseoil

Active Member
#71
#71
A friend's son suggested drilling the fuel cap & it worked! Ran it up to 8720 & then pulled the plug after a few runs to check tune. Here's what I found... Always something to do. Longer post in my site, but you get the idea. Plug-Int-1.JPG
 
I74

I74

Well-Known Member
#75
#75
Went & checked out your site again.
Looks like you got lucky with the piston & plug.:eek:
Really nice piston in that engine !
It's amazing more times than not,, about how little things like cap venting, affect performance ect ....
Would love to see a vid of that engine @ high RPM 's.:p

I think at this point if that bike was mine, I would be looking into some kind of 2 speed set up.
That would be really trick! ;)
 
noseoil

noseoil

Active Member
#76
#76
Ole, stock valves, rockers & retainers. Yes, I need to look into SS valves as I'm pushing my luck now. I'm using the original valves from the original build. Have another set I can use, but they're still just factory. The SS valves would be a bit stronger, correct?

I74, sooner or later I'll get a video of the motor on a run so you can see it. Lucky is right. Need to look at things again now, so the motor doesn't eat itself. I'm sending off for an oil analysis soon, to see how the main bearing is holding up to the abuse. Not sure what they'll find in the stuff, but there's bound to be some metal in there floating around.
 
I74

I74

Well-Known Member
#77
#77
Found this oil @ Wally world awhile back, & have been running it in my stuff.
It's cheap, & seems to work pretty darn good.
Definitely not break in oil though. ;) 100_5485.JPG 100_5483.JPG
 
TheDullCarbide

TheDullCarbide

Active Member
#78
#78
I74 said:
Added,,
Another trick is to long gate the mounting holes on the coil pack, & move/ advance it closer to the rotation.
You might gain a couple of degrees or so advance in just doing that.
Click to expand...
I measured 1 extra degree
I74 said:
Went & checked out your site again.
Looks like you got lucky with the piston & plug.:eek:
Really nice piston in that engine !
It's amazing more times than not,, about how little things like cap venting, affect performance ect ....
Would love to see a vid of that engine @ high RPM 's.:p

I think at this point if that bike was mine, I would be looking into some kind of 2 speed set up.
That would be really trick! ;)
Click to expand...
Maybe this whole problem is caused by valve float and not air density? Maybe??
 
ole4

ole4

#79
#79
the stainless valves use split retainers and a round grove which are stronger and do not creat a stress riser like the sharp edge on a stock valve where the retainer goes on. I am surprised turning almost 9K you did not drop a valve with the stock valves and retainers.
 
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