Tuning the Tunebug, now with video

[drooartz]

Okay, time for my resident experts to chime in with some help. Tunebug is well worn, so I know I'm up against some deeper issues.

Idle is at 1000rpm (about as good as I can get). Mixture is 8 flats on front, 6 on rear. Here is the idle sound:

https://www.drooartz.com/public/tuning/MVI_0002.AVI

Pushing up the pistons in either carb causes the RPM to raise a bit and stay there.

What do I need to do?

 

[Trevor Jessie]

What happens when you try to lower the idle? Just dies?

You may not get it any better if the throttle shafts are badly worn.

 

[14dna]

Sounds like it's drawing a little false air, (vacuum leak). I'm agreeing with Trevor, throttle shafts may be the cause. I also noticed some black smoke from the exhaust. This is an indication of rich mixture, but if the shafts are worn you will never lean it out properly.
Dave

 

[Baz]

You did the static timing, did you do the dynamic?

 

[drooartz]

The shafts are probably worn, how can I check?

Here is take 2 -- both carbs at 4 flats (keep in mind I'm at 5550' elevation)

https://www.drooartz.com/public/tuning/MVI_0003.AVI

Sound isn't that great, but the exhaust seems more even. RPM still rises a bit with the piston-lift method, but doesn't rise more if I hold the piston up that little bit.

 

[drooartz]

Static timing only, about 7deg BTDC. There doesn't seem to be any spec for dynamic timing, and I'm not sure I can read the mark and try and shoot it with my timing light (which I've never used, but it is not one of the adjustable ones).

 

[Baz]

Yeah, I think 8* dynamic, doubt it'll make a ton of difference.
#2 does sound better.

 

[drooartz]

Just tested out my timing light (an old HeathKit one my father-in-law made, very cool). I was able to check the dynamic timing. About 10 degrees (maybe 9) at roughly 1000RPM. Vacuum line disconnected from dizzy, and plugged at the dizzy. Increase in throttle and the timing advanced as it was supposed to. Cool.

 

[cdsmith]

The shafts are probably worn, how can I check?

Maybe try spraying some carb clearner or WD40 around throttle shafts - change in idle will indicate vacumn leak.
Hope this helps.
cd

 

[regularman]

My pinto carb gives no such problem /bcforum/images/%%GRAEMLIN_URL%%/wink.gif Wish I could help but I no nothing about the dual carbs. T'is running rich by the look of the smke though.

 

[leecreek]

Due to your altitude, I think I would try a leaner needle set and see what happens.

 

[jlaird]

I bet it is throtle shaft leakage.

With engine running squirt a bit of carb cleaner at each point where shaft goes into barb body. If RPR raises you have a leak. Your four five flat adjustment is also an indication, air has to come from somewhere to suck that fuel it is like the chokes are open just a bit all the time. AIR LEAK...REPEAT AFTER. ME AIR LEAK....READ MY LIPS, AIR LEAK. Some time over a beer Drew, ask me how I know.

I also think that engine sounds tired, very tired.

 

[drooartz]

Jack, this engine is indeed very tired. I'm asking a lot of it, I know, but it needs to go one more summer. The 1275 just isn't ready yet, and probably won't be until much later in the year (unless one of you wants to donate to the cause /bcforum/images/%%GRAEMLIN_URL%%/grin.gif ).

Really, everything on the Tunebug is tired. The dizzy is probably worn, I'm sure the carbs are worn, and the engine is certainly worn. It's the original motor, and I'm pretty sure it has never been rebuilt, though there's no way to know for sure. The only real solution is rebuilding all the mechanicals, which is my plan for later in the year.

 

[jlaird]

Understand Drew, very well. Just trying to help a bit.

As always do the best you can, if you don't stress that engine too badly it will last the summer with any luck.

 

[drooartz]

I don't venture very far from home, mostly just terrorizing the neighbors. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

My parents will be out in a week, and I want to be able to take them for a spin. After that, I'm pretty content just to start the rebuilding process even if I can't run it for a while.