engine and drivetrain Engine Bogs On Decelleration

[zinz]

After searching the far reaches for obsolete bits and pieces and finally getting my dual Solexes jetted correctly (Ruddies-Berlin had the goods) I am still experiencing a persistent bog after deceleration.  It's not lean-popping. The carbs are loading up (too much fuel). 

 

It's my understanding that during hard deceleration, the fuel pump (mechanical) is whizzing away and overloading the carbs.  I presume the pressure spikes and forces fuel past the shutoff valve and overfilling the bowl.

 

It can be a real PITA when downshifting and then trying to get right back into the throttle....stumble, stumble...

It's an even bigger PITA in traffic and running up on a redlight (why do they all change RIGHT in front of me??) The carbs get loaded up, then engine bogs down, and I have to blip the throttle until it clears itself.

 

So... sounds like I need a fuel pressure regulator between fuel pump and carbs.  Which one do y'all suggest?

 

Here's my setup in case I'm mis-reading my problem...

 

'71 M10 with 121 head

292 cam

original flat top pistons (low comp)

Hi amp alt

Bosch 0-231-129-033 dizzy (Ti dizzy, with tight shaft and appears to have good curve characteristics)

Hot Spark igniter

Red coil

Ignition set to about 25 degrees at 2200 rpm. (checked total advance at about 37 degrees at 3000 rpm?)

Long tube header

Twin Solex 40DDHTs (freshly rebuilt, with tight throttle shafts)

jetted:

55-90 Pilot jet

130 main

90 Air Corrector

Original velocity stacks, running angled UniFilters (easily clears brake booster)

Original 90 degree mechanical fuel pump (also freshly rebuilt)

 

One last thing... I'm getting a strong gasoline smell after it sits (like my POS Weber 32/36 used to do in the heat of the summer when it would vapor lock)  There are phenolic spacers between carbs and manifolds.  I really don't think it's vapor locking, but maybe it is.. I do have to pump the gas several times in the AM to get her started. IDK...  I'm also seeing fuel on the seal of the gas cap (like it sloshes up the fill pipe..) but it isn't leaking down the fender, or anything.

 

Ay suggestions??

 

 

 

 

 

 

 

 

 

[Hans]

Original cars ran nicely without pressure regulator. How did you set the float levels after rebuild?

[bmwfan]

Look at the malpassi Filter King fuel pressure regulator . IE has them at a decent price.

[Mike Self]

I'm not that familiar with Solex 40DDHTs and how they differ from the 40PHHs that the factory fitted to 2002ti's, but  I suspect they would be jetted the same.  Have you checked your jetting with what the factory calls for in the shop manual?  From your pictures it appears you're running the early style fuel pump (the kind that can be dismantled and rebuilt), which is what the factory ti's used, so you should be able to run without a pressure regulator--the factory setup did. 

 

Were I you, I'd suspect something either in the carb setup (jets, float level, etc) or a leaking needle valve that's allowing fuel to pass even when shut off. 

 

mike

[zinz]

Hans,

 

During rebuild, I had no way to properly bench-test the float level (using the elevated fuel reservoir) so I've checked the float levels after installation by opening the top of the jet cover and dipping a thin bamboo skewer past the air corrector jet and measured the wet level against the top of the carbs and to the mid-point of the venturis.  The Solex tuning books say this is where the fuel level should be... The float level is easily adjusted with the fuel inlet.

 

As for the jetting, Mike... Alpina used these carbs in aftermarket applications.  I found several references with their specs. http://translate.google.com/translate?hl=en&sl=de&u=http://www.02-club.de/technik/solex.htm&prev=/search%3Fq%3Dsolex%2Bddh%26hl%3Den%26lr%3D%26rls%3DGGLC,GGLC:1969-53,GGLC:en

 

I've also consulted with several FAQ guys and Jurgen Ruddie in Berlin and believe I have the jetting pretty close (don't have a WBO2, but the plug colors have been good during road tests). 

 

Carbs came with a 110 main and 40/60 pilot jet.  I went to 120 main and was still lean; I'm now at a 130 and midrange is very strong.  WOT pulls strong to redline, so Air Corrector must be good as well.  The 40/60 Pilot Jet was far too lean.  Idle jet screws made no difference in idle speed and were turned out to 3 1/2 - 4 turns.  Ruddies had the bigger, 55/90 Pilot Jets and now I can make adjustments at about 2 1/2 turns for highest idle speed. 

 

Synchronization is spot-on using a Carb Tune.

 

I rebuilt the fuel pump and it was in very good shape.

 

I spent a long time rebuilding both carbs, making sure every last detail was inspected and cleaned.  The leaking needle valve may be the culprit...perhaps it has a tiny piece of debris in the orifice.

 

I was hoping to avoid removing them, but I may need to tear them apart and inspect them thoroughly again.  Something is amiss and the fuel smell in the garage after shutdown is pretty bad.

 

Thanks for the input, I appreciate any help I can get.

[ray_]

Your fuel tank is not leaking at the seam, right?

 

There! That's all I know about carbs!

 

[TobyB]

I have had 'overzealous'  mechanical fuel pumps, too.  The spring sets the pressure, and it can be too strong...

 

Try a different pump!

 

t

[ray_]

I have had 'overzealous'  mechanical fuel pumps, too.  The spring sets the pressure, and it can be too strong...

 

Try a different pump!

 

t

 

Or a pressure gauge?

 

[eurotrash]

I tucked in a basic regulator here.  And  mini pressure gauge up stream along the frame rail, so I could tell if my pump ever decided to crap out..

 

 

[Hans]

You could try a regulator, but with 40 DCOEs, I noticed excess pressure more at steady cruise - engine got jerky. Never had a problem with original Solex PHH - it was the spindles that finished them. There is a process for setting float levels in the shop manual that uses some fancy plumbing and graduated flasks, etc. Somewhere I found the target depth of fuel in the bowl. Right now, can't remember where. I had 40PHHs rebuilt, but couldn't get them to run. I suspect it was the float levels. You might Google around for static fuel level in the bowl and use the chop stick method to measure. Your problem sounds like it might be related to float levels too high. Or needle valves not shutting.

[zinz]

I can always count on Ray to give great carburetor advice....he's a good one....  But no leaks on the fuel tank seam.

 

As for steady state symptoms, I am experiencing a flat spot right around 3400rpm at steady driving (about 60-65mph on the highway) It only happens at that rpm level.  I think it's related to the transition from the progression circuit to the mains. Kind of a pain, but not a huge deal.

 

As for setting floats the shop manuals talk about the apparatus that I have no access to... So I'll continue to use the chopstick/bamboo skewer method and try to get a more accurate reading.

 

I think a pressure regulator will be easy enough to try as well... they can be pretty expensive (at least the ones suggested here).  I do like the stealth mounting of the Mr Gasket regulator under the carbs, but I'm not sure I route the plumbing like that.

 

I'll work on things more in the next few days and try to sort something out.

 

Thanks again for the advice... even yours, Ray...

 

[Hans]

http://www.bmw2002faq.com/topic/80670-solex-phh-40-float-level-procedure-and-setting/

 

3/4" sounds faintly familiar

[ndog]

be carefull adding any extra stuff to your fuel system(like gauges,regulators,excess connections=more failure points.(K.I.S.S)

i bet your pump is exceeding that head pressure test as seen in the photo above.

If you would like to try a regulator, I have a webber one you can test with..... pm me

good luck sir

[KFunk]

I have a similar problem (40 DCOEs with IE electric pump, no reg), but it's not nearly as bad as yours.  The only time mine does it is at autocrosses, when I have to stop for a time slip.  It's a pretty huge transition from high demand acceleration, to hard braking.  It floods and stalls out if I don't hit the throttle.  No problems at all on the road, and often not even a problem at autocross.

Yours seems way worse for some reason.

[ndog]

^call steve nelson at TEP

carter fuel pump makes the exact pressure 40dcoes require(no regulator)