Bad Carb Slide Diaphragms!

[Gearhead]

I've been chasing poor mileage on my 87 for the year I've owned it. GeorgeS has written more than once that holes in the slide diaphragms will cause poor mileage and are common at this age. I finally pulled one this morning and guess what - it's bad! (Almost looked as if they had never been removed before.) Several obvious cracks, light shines right through them. The slide itself, needle, and jet looked OK. They are SOOOO easy to pull on this bike that there was really no excuse to wait so long.

 

What's weird is that the bike runs fine - no stumbles or hesitations, revs right up to redline, plugs are the appropriate color. Is this common, that they don't affect driveability, but hit the gas mileage? It seems like this problem would cause a lean condition, which isn't good for the engine but in some cases can actually HELP mileage...

 

QUESTION: Are the coasting enrichener diaphragms also commonly disintegrated? One guy had that problem here recently - anyone else? What kind of problems will that cause? They are harder to get to...ughhh.

 

COMMENT: Some have written, indeed I have done so myself, something like, "I watched the slides with air filter removed and engine running, and they all seem to be doing the same dance, so they are probably OK." I can tell you, this is NOT a valid test! In fact, just this morning, I repeated this "test" with a now-known bad diaphragm, and they still appear to dance the same. Maybe they are all cracked exactly the same.

 

Jeremy

[GeorgeS]

When you pulled the one out, did you note if the " tamper proof " screw, (one on each diaphram cover ) was still untempered with ??

 

If so, then your's have probably never been removed.

 

I think the best price, is about $85 apiece, but forgot which supplier that was.

 

I would say when you replace the main diaphrams, do the enricher ones also.

 

Also, are your " lead" seals, ( below, + center of Dia covers ) still Installed, over the Idle mixture adjust needle valve's ??

 

If so, pull out the lead seal, and adjust the " Idle mixture needle valves " to 2 1/4 turn CCW from full closed. ( carefull not to damage needles, when turning CW to the full closed position )

[rhncue]

When you pulled the one out, did you note if the " tamper proof " screw, (one on each diaphram cover ) was still untempered with ??

 

If so, then your's have probably never been removed.

 

I think the best price, is about $85 apiece, but forgot which supplier that was.

 

I would say when you replace the main diaphrams, do the enricher ones also.

 

Also, are your " lead" seals, ( below, + center of Dia covers ) still Installed, over the Idle mixture adjust needle valve's ??

 

If so, pull out the lead seal, and adjust the " Idle mixture needle valves " to 2 1/4 turn CCW from full closed. ( carefull not to damage needles, when turning CW to the full closed position )

 

The diaphragms may have went up some but Rick Hafferkamp of Buckeye Performance was selling them for around 55.00. You usually can tell when the enrichner diaphragms go bad as the bike will pop through the carbs on deceleration.

 

Dick

[Gearhead]

Thanks. More input welcome. Yes, my tamper-proof screws looked unscathed, and it just generally looked not-messed-with, except that one regular screw had been replaced with a different type, which of course indicates that it was removed once. The pilot screw plugs have already been removed.

 

Will bad slide diaphragms cut into fuel mileage but allow the bike to run OK? Has anyone else experienced this?

 

Other than the popping on decel, is there any other ill effect of bad enrichener diaphragms? Does that create a vaccuum leak? Or is it just as it the coasting enrichener circuit was not there? It only comes into play on the overrun, right?

 

Jeremy

[GeorgeS]

I never had them out, and no problem with them, so can't say.

 

I was not haveing problems with the main ones either. I just opened one up and found some holes, so I decided to change them, as it was December, and had nothing else to do , except put up Xmas lights.

 

On the mixture screws, as you screw them into full closed, Keep count of 1/4 turns so you know where they were set, before you Open them to 2 1/8 turns. Thats the aggreed upon correct setting.

No info on that in Service manual.

[Gearhead]

GeorgeS, thanks for your help.

 

COASTING ENRICHERS - has anybody had any reason to replace those diaphragms? Well, I know one of you has - anybody else? Looking at the carb circuit diagram in the manual, it appears as if this is a normally open path for air to enter the pilot circuit, which the diaphragm closes under the high vacuum of overrrun, causing enrichment. Emissions only, I think, so if I don't mind a little popping on overrun, I would think that having them open all the time and sealing off the vacuum source would work. Opinions?

 

SLIDE DIAPHRAGMS - George, you said you weren't having drivability problems with your bad diaphragms - how about a mileage drop? Did replacement do anything for your MPG?

 

Thanks again,

Jeremy

[GeorgeS]

I would say about 5 mpg better. But that subjective

 

My diaphrams, had about 3 holes each in three of them, and none in the 4th one.

 

Milage was about 48K. I bought the bike new in 93.

 

As I said , it was DEC. so was not going to put the old ones back in. so ordered a new set.