Lemans I Starting Issues

[blackcat]

I have been trying to get this newly rebuilt engine running for a few days now and I'm at a cross road.  Just for background, rebuilt engine with new Raceco P3 cam, original 36mm carbs that I rebuilt and I'm running points because the Dyna black box was a problem, which has been sent back to Dyna.  I have checked the flywheel timing marks with a degree wheel and the retard mark was slightly off so I relocated the distributor based on that new mark.

This is what happens, the bike will start with starter fluid and immediately go to redline, and restarting will happen if I cover a carb mouth.  I have disconnected the chokes and both accelerator cables with the same result and the slides are not hung up and it is both carbs as I've pulled a plug on one one side then the next with the same race to redline. This race is like seconds and then I kill the engine.

Tomorrow I'm just going to pull the carbs from the 1000S and see if that solves the problem. I haven't pulled the carbs to look at what is going on inside but I just want to narrow my problem by installing a known non-problem set of carbs. 

Any suggestions? 

[Chuck in Indiana]

And the slides are sitting down against the stops? <scratching head>

[lucian]

Not familiar with the 36mm 's but the square slides on my v50 can go in backwards and prevent them from seating properly against the idle screws. Must be getting too much air somewhere. As Chuck said , make sure the slides are seating on the idle stop screws.

[blackcat]

And the slides are sitting down against the stops? <scratching head>

Yes, and the needles are not hung up either

[berniebee]

Throttle stop screws should not be screwed all the way in...

[blackcat]

Not familiar with the 36mm 's but the square slides on my v50 can go in backwards and prevent them from seating properly against the idle screws. Must be getting too much air somewhere. As Chuck said , make sure the slides are seating on the idle stop screws.

I’ve backed off the idle stops completely, the chokes were my first guess but I disconnected them from the cables and let them drop in the barrels.

[lucian]

I would check the slides and make sure they can only go in one way, if not reverse them. i think most of the round slides have a indexing  groove to prevent this though. Did you replace the original slides when you rebuilt the carbs?

[blackcat]

I would check the slides and make sure they can only go in one way, if not reverse them. i think most of the round slides have a indexing pin or groove to prevent this though. Did you replace the original lides when you rebuilt the carbs?

The slides have been changed and they can only go in one way due to the pin and the plunger for the pumper.

[lucian]

That may be the problem , the newer slides have a different ramps on the side for the idle stops. unless modified they will not allow the slides to drop fully against the stops. see below.

http://www.mgcycle.com/index.php?main_page=product_info&cPath=62&products_id=5087

[blackcat]

That may be the problem , the newer slides have a different ramps on the side for the idle stops. unless modified they will not allow the slides to drop fully against the stops. see below.

http://www.mgcycle.com/index.php?main_page=product_info&cPath=62&products_id=5087

Hmmm....I’ll have to look at those slides. The ones I installed are not brand new, but older slides with little wear but I will check them out. It still doesn’t explain how the revs shoot all the way up to redline.

[lucian]

I agree, you'd think that would just result in a high idle. Must be air getting by somewhere.  Maybe try the old slides?

[blackcat]

I agree, you'd think that would just result in a high idle. Must be air getting by somewhere.  Maybe try the old slides?

The old slides had some problems, so that won’t work.

[Canuck750]

Hmmm, sounds some what like to problem I had with the similar carbs used on my Laverda 750 SF, this picture from my LeMans rebuild



The LeMans carbs gave the bell crank tops, the Laverda do not but the placement pf the slides with the plastic guild tang, the spring location etc, is a bit finicky.

I messed with the Laverda carbs for a year, installed all new internals including the dreaded new slides with the small ramps and finally fist installed a brand new pair of Dellorto carbs. I would seriously consider just installing a new pair, the Dellorto's just wear out but that should not be the problem you are having. To be at full throttle the slides would need to be wide open. Have you visually confirmed the slides are at fully shut position (less a tiny opening for idle) ?



I don't think this has anything to do with full throttle but have you set the float height with the carb mouth on a flat surface, floats vertical?

[blackcat]

“To be at full throttle the slides would need to be wide open. Have you visually confirmed the slides are at fully shut position (less a tiny opening for idle) ?”

I don’t have filters or the velocity stacks on the carbs and at rest they look just like the ones above.   If the carbs on the 1000S work, then I’ll play with the existing carbs some more but I’m sort of resolved to getting a new set of carbs which I really don’t want to do but it has to run right.

[chuck peterson]

Main and idle jets mixed?

If no one has guessed that I’ll put five dollars down..

A 140 in your idle spot...or whatever your main is, but wrong passageway. Would that run the rpm up that high?

[Antietam Classic Cycle]

Main and idle jets mixed?

If no one has guessed that I’ll put five dollars down..

A 140 in your idle spot...or whatever your main is, but wrong passageway. Would that run the rpm up that high?

On PHFs, the jets can't be mixed up as they have different thread sizes (unlike VHBs).

[blackcat]

I think there is a problem with the chokes, only because when i use the flip chokes on my other bikes the RPM shoots straight up and they work right. I think these are sucking too much air even though I’ve replaced both plungers.

[wirespokes]

I wonder if the cam timing is off?

I don't think leaving the vacuum ports open would do it...

I don't believe the PHM 40 Dells will mount to spigots for PHFs.

[Rolf Halvorsen]

I once worked with a 850 Eldorado with similar problem like yours. The main problem was that there was a "hole" in the thin walled ceiling above the floater. When you say that covering the mouth of the carb will help - that is what reminded me of my earlier episodes.

Check yours. It could be a tiny hole in one of them.

Rolf

[blackcat]

I wonder if the cam timing is off?

I don't think leaving the vacuum ports open would do it...

I don't believe the PHM 40 Dells will mount to spigots for PHFs.

I’ve checked the timing with the degree wheel and unless I’m wrong that isn’t the problem. I could easily be wrong, which is why I decided to swap the carbs.

The 1000S has 36mm carbs, so that will tell whether it is the timing or the carbs.

[blackcat]

I once worked with a 850 Eldorado with similar problem like yours. The main problem was that there was a "hole" in the thin walled ceiling above the floater. When you say that covering the mouth of the carb will help - that is what reminded me of my earlier episodes.

Check yours. It could be a tiny hole in one of them.

Rolf

I’ll have to take the carbs apart and take a look. This bike has been sitting apart for probably 10+ years in south Florida in unknown conditions, but based on what I got it couldn’t have been great.  Thanks, I’ll take a look.

[PeteS]

How many miles on the bike? My '76 has about 45K with the original carbs and it still starts and runs like new. Other than swapping main jet sizes and some of the rubber bits everything is original.

Pete

[blackcat]

How many miles on the bike? My '76 has about 45K with the original carbs and it still starts and runs like new. Other than swapping main jet sizes everything is original.

Pete

There is 15,000 miles on the clock but I have no idea if that is accurate. The clip on the piston pin wasn't originally installed correctly so this is what we guessed why it was pulled apart and left to sit for many years. The original cam was toast too.



And this was after it was bored out in hopes of installing a new set of pistons.

[Frenchfrog]

You've surely made sure the advance /retard mechanism is working smoothly and not sticking....carb slides move up and down smoothly? I've had this on one of my BSA's but can't remember what it turned out to be...

[blackcat]

You've surely made sure the advance /retard mechanism is working smoothly and not sticking....carb slides move up and down smoothly? I've had this on one of my BSA's but can't remember what it turned out to be...

I checked the advance mechanism before installing the dizzy and then I checked it again when the dizzy cam stopped spinning because the pin holding the gear failed(I found the pin head on the cam gear)  and the carb slides open and close really well.

[blackcat]

That may be the problem , the newer slides have a different ramps on the side for the idle stops. unless modified they will not allow the slides to drop fully against the stops. see below.

http://www.mgcycle.com/index.php?main_page=product_info&cPath=62&products_id=5087

OK, I pulled the slides and the ones in there are not modified as they sit about 12mm above the tunnel whereas the ones in the 1000S are 6mm above the tunnel at rest.  I’ll modify the slides and that should address the high RPM but will that cover the entire problem?

[moto-uno]

  One has to be careful looking for crystal balls around here ! Let's see if the next move corrects this .  Peter

[moto-uno]

 A picture they say , this is from my Le Mans 2 with 40 mm dellortos . This is a picture of the throttle slide
position at idle ( it idles well ) . If yours is more than a hair higher than this , it MAY be part of the trouble .
Peter

[blackcat]

OK I got it running, now it's just jetting, needle,etc. The other problem that added to the racing was that the new Tommaselli throttle stops had to be drilled out because they weren't letting the slides go all the way down.  Now both slides click back onto the base of the carb.

The engine is starving for gas so either it's the main jets, float height or all the usual suspects. I did move the clip on the needle but that did nothing so I'll take the carbs apart tomorrow and see what's up.

Thanks all.

[lucian]

From Guzziology.