Ace 90 goes on strike

[matt glascock]

Thrown, that's one of the mystery features. When I originally confirmed proper jetting, the plug chops read nice tan/brown. Now more black. That's a great thought, Pop. I will give the stand pipe and vent tube special attention. Also, before I dunk the carburetor, do I need to worry about the phenolic heat block being damaged by immersion in the solution? Thanks guys.

[thrownchain]

Carb cleaning solution----metal only. Don't risk anything else. Will melt some rubber parts, not sure about the block, but why risk it?

[thrownchain]

Maybe a hint that the clutch side seal is starting to leak?

[Dale]

It does sound like a rich pilot circuit. Not enough air in the mixture. Either the air circuit is plugged or the pilot jet is too large. Could the jet have been enlarged by over aggressive cleaning?

I think you could eliminate your thought on the valve leaking by shutting off the petcock while it is still running well and then keep it running for 30 seconds or so before shutting it off. Now will it restart?

[taber hodaka]

Loads up and you have to run full throttle with the fuel off. I would install a new needle valve and seat also check the float setting, then adjust the carburetor. I don't mind a black plug if it doesn't foul.----------------------- Clarence

[matt glascock]

Thanks Thrown. That was my concern. In the MIC VM20 the phenolic heat block is built into the carb outlet and I really don't want to try removing it even if it is removable. Ace 90 carbys are scarce. I have been keeping my eye on the oil level and it has not dropped at all. Leak down test confirmed the motor is air-tight.
Dale, there is sure a possibility I could've distorted the pilot jet with over-aggressive cleaning. I think the proper move now is to change out the pilot jet if I can source one but I will try your suggestion.
Clarence, I have confirmed proper float height. Along the line of Dale's suggestion, maybe the next move is to score a new needle valve and seat. Maybe its time for a ground-up carb rebuild. NJ/JN,PJ, MJ, the whole schmeer. I'll see if Terry has VM20 rebuild kits with stock components for Ace 90 application. Thanks guys!! I'll report after I get this all sorted.

[viclioce]

Matt. Looking at the 90 carb on Terry’s parts list, I don’t even see a pilot jet listed for the OEM 90 carb. Only the pilot air screw. Go look at the carb parts diagram. It only shows a main jet and the float needle assembly & a pilot air screw (see attached).

If you have a pilot jet, maybe your carb is an early 100 VM20? It’s interesting that the 90 lists a VM2000 and not the typical VM20 listed for the 100’s.

If there’s a pilot jet for the OEM 90 carb, can someone explain why it isn’t shown on the parts list??? Thx. Victor

[matt glascock]

Great question, Victor. Back in the dark ages, I ditched the Mic carbs on my race bikes for either Amal or Bing instruments so I'm not sure about the VM20. I'll leave that to someone much smarter than me.

[thrownchain]

If you go to the fiche of the rebuild kit, the pic shows a pilot jet. The stock fiche of the carb does not.

[viclioce]

Well that’s the explanation needed! Thanks Thrown! Knew there had to be some explanation! Didn’t seem likely there wouldn’t be an idle circuit. Victor

[Dale]

The parts schematic does not show a pilot but the specification sheet lists a 25 pilot.

Another thought Matt... what about the choke (fuel enrichment) circuit? If the seal it not good, it can create the richness too. Try putting pressure on the lever to see if it makes a difference.

Thrown's suggestion of right side crank seal makes sense too. Hopefully it won't come to be that.

[matt glascock]

Dale, if it was a clutch-side seal, would that automatically result in an air leak? The leak-down test confirms an air-tight motor. It doesn't seem to smoke excessively or smell like anything other than Yamalube 2R premix. I've been through the clutch-side seal failure before and there was a difference in the exhaust smell. Man, I hope that's not the case! The enrichener was a little suspect insofar as the rubber was a bit hard, but not cracked. I'll try your suggestion and see if the seal is at fault. I have a few plungers in my carb stash so it might be a good move to replace this one with the pick of the litter. Great idea. Getting back to Victors inquiry, my carb has a pilot jet and it is indeed a 25. Many thanks fellas!! We'll get this sorted out yet.

[viclioce]

Thanks for the confirmation, Matt. Makes me wonder if there are other parts lists for other Models, missing various parts? I use the parts lists regularly to advise & confirm whether I’m missing a part, or if someone else might be. I just reminded Alan again to look at the parts list to identify if you have the correct part for his bikes. He now has an Ace 90, Ace 100 B+ and a Super Combat. Victor

[Dale]

I think a passing leak down test would indeed rule out a fault in the clutch side seal.

[thrownchain]

If it passed the leak down test and the timing is spot on, then it's the carb. Unless the exhaust pipe is getting plugged up.......

[matt glascock]

Grrrr.... So I pulled the spark arrestor out of the pipe and burned out. I did nothing special to the pipe other than a visual inspection and a blast of compressed air. That brings up a good question. How do you deep clean a chrome pipe? All my race bikes get the pipe cooked at least yearly and for the TM multiple times as it runs bean oil. I dust em off, squirt some manifold paint on, and off we go. Its not fuel proof, but the paint gets nicked up anyway, so what the hell. What is the safest way to cook a chrome pipe?

[Dale]

Buried a ways down in this other post is a description of how I cleaned my Ace 90 pipe using mineral spirits. The next time I do it I will add a pre-treatment with oven cleaner.
viewtopic.php?f=1&t=765&p=3618#p3618

[matt glascock]

Very helpful, Dale. I'm going to go that route with this pipe. It is in good shape and I don't want to discolor the chrome with the torch. Thanks Dale!

[Dale]

Very helpful, Dale. I'm going to go that route with this pipe. It is in good shape and I don't want to discolor the chrome with the torch. Thanks Dale!

Matt,
If you don't already have a tub large enough to do the soaking, the large plastic tub that Home Depot has for mixing premix concrete works great. You can set it up at a good tilt so that just a gallon (maybe two) will submerge it completely.
Dale

[Bullfrog]

I'm getting just a bit of a giggle about how the tone of this thread has changed. It started out with an Ace 90 which, "Runs like a top till I shut her down." - and has kind of morphed into something more like, "this machine has been giving me hints in several ways that it is not happy and may go on strike or outright quit before too long."
Ed

[Dale]

Yup, I've considered this too. Why does it run okay and then won't restart? I can believe that it could be the carb loading up either while idling or with the motor off. If it is too rich at idle, it should be noticeable. I still wonder too about compression or maybe a weak ignition situation.

I have several Hodaka's that if I run them rich on the pilot, they will not want to fire when cold unless you bump start them. But, they will easily restart when warm. Just the opposite of Matt's Ace 90.

[thrownchain]

Best to address one thing at a time. Fix it, try it. If you do multiple things and it works you won't know which single thing was the issue.

[matt glascock]

I'm going after the carb as the culprit. The pipe was an aside. I agree Thrown. I'm sorting the carburetor first. Captain, did it occur to that this reporter is sending our community on a wild goose chase???