Timing issues that Fred's guide does not discuss..

I am working on my newest moped, a 1986 Trac Hawk, and I believe the timing needs adjustment. Here are the symptoms:

-Once jetted properly, the moped idles like a charm but when acclerating/cruising the rpm's fluctuate rythmically, and as a result power is very apparently sacrificed. The rpm's will bounce back and forth from normal rpm's to abnormally low rpm's and then back up again, so on and so forth. The best way I can describe this is like expressing the rpm's as a sine or cosine curve, with each period being about one second long.

-Uphill this effect is increased dramatically to the point where the moped slows down and eventually stalls, rpm's fluctuating all the way.

All I can think of that can cause this is the timing is out of adjustment. What effect on performance does advancing the timing from stock have? Retarding the timing? What do you suggest I do to solve this problem?

Re: Timing issues that Fred's guide does not discu

Leon Swarmer /

Great description. Interesting problem. I'm betting it's not timing, but fuel supply. I'm eager to hear other ideas.

Leon

Re: Timing issues that Fred's guide does not discu

I don't think this is timing, it sounds more like a fuel mixture issue. As far as rich or lean, you might be able to tell by the sound.

If the motor makes a hollow, sucking noise, it's lean - if it makes a muffled, blubbering sound it's rich. Of course, this is all relative to how it sounds when it's running correctly.

Are the stock airfilter, aiirbox and exhaust installed? Why did you change the jet(s) and which way did you go - larger or smaller?

Re: Timing issues that Fred's guide does not discu

I have stock everything except that the airbox/filter is missing and it has been absolutely impossible to find one, so I went ahead and bumped up the jet one size at a time until it started behaving correctly. It was 56 stock and I stopped upjetting at 66. This is an encarwi carb which uses the same jets as bing carbs. It had the same problem with the 56 jet that it does with the 66 jet, except now the engine doesn't cut off at random from being too lean. Because the fluctuating of rpm's occured at both jet settings, I am not sure that it is the fuel/air ratio. Unless you can present another reason why that might be it.

Re: Timing issues that Fred's guide does not discu

If the timing is set to the timing marks, that is all you can or should do.

I think that the exhaust is choked up. Remove the header pipe and clean it out (I assume that you cleaned the exhaust port when you had the engine apart.) re-install it and remove the muffler. Try running the engine without the muffler (use earplugs) and see if it runs clean.

Re: Timing issues that Fred's guide does not discu

One problem here is that, believe it or not, there are no timing marks on the flywheel of the engine casing. nothing. Which adds to the timing enigma and whether or not it is set correctly. The muffler has been cleaned already.

Re: Timing issues that Fred's guide does not discu

What do you do if there are no marks?

Did you clean the exhaust outlet leading from the cylinder head to the exhaust header too? Mine was pretty cruddy in there.

Re: Timing issues that Fred's guide does not discu

With the stick in the sparkplug hole find top dead center and then mark the flywheel. I would use a centerpunch to make it permanent.

The flywheel on my Minarelli V1 ia just about 4" in diameter.

The timing mark is 7/8" before TDC. This is a starting point.

Rotate the engine backwardss and make a mark 7/8" back from TDC. Use this mark to time the engine.

If it runs, you might have to adjust the timing mark to give you the best run.

Maybe someone with the same model engine as you have can measure the distance between their TDC and the timing mark.

Let us know if it runs.

Re: Timing issues that Fred's guide does not discu

thanks

Re: Timing issues that Fred's guide does not discu

Steamboat Aka J. R. Stevens /

Hey Pete, It sounds like you are pulling the float bowl dry when the engine is increasing RPMs and the bowl efills while the RPMs are decreasing. ie. Not enough fuel flow from the tank to the carb. First, try running with your gas tank cap removed.If that doesn't work, disconnect fuel line from carb to make sure fuel flows freely.Keep us posted. Jim

Re: Timing issues that Fred's guide does not discu

Leon Swarmer /

My former Garelli had Steamboat's issue after it was ported by the PO.

They increasd the bowl capacity by putting two holes in it and running another piece of fuel line between them. Not a great increase, but it solved the problem.

Leon

Re: Timing issues that Fred's guide does not discu

Steamboat Aka J. R. Stevens /

Hey Pete, If your float is adjustable, It may be set so low the bowl never fills up. Jim.

Re: Timing issues that Fred's guide does not discu

That's a good idea. Are there any possible negative consequences for increasing the float bowl size? The more gas the merrier? Do you think that running my ped without the airbox and upjetting as a result can cause problems related to float bowl size, or is that not enough of a fuel consumption increase to even matter?

Re: Timing issues that Fred's guide does not discu

Re: Timing issues that Fred's guide does not discu

Hey pete, did your problem just devalope, If so I have the same or very similar problem on my Mobyx.

Was running fine then Started revving high and low, now its doing it even at idle.

I have been through the carb and have just taken the exhaust off for cleaning. Keep me updated please.

Re: Timing issues that Fred's guide does not discu

No, this I've had this problem since I got the moped a few weeks ago.

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