Low RPM trouble. Jetting?

[Andi/DFL]

hi,

took the  bug for a ride, first time this year. I have some serious problems when accellerating at low RPMs (traffic lights, etc). The engine splutters and misses, sounds like a carb problem to me. So I swapped the 70 idle jets (mild 1776, small valves, 48 IDAs) for 55s, just to check, if the problem gets better or worse. Didn't notice a difference. This is new to me, I did not have this kind of problems before.

I've had the carbs completely stripped in the winter and mainly cleaned everything and replaced some gaskets and replaced the F7 emulsion tubes with F11 ones. Carbs respond fairly good to the idle screws, engine runs very smoothly at idle and the problems seems to occur only when driving. If I launch at higher RPMs, there is no problem. NO - this is not a solution :-)

Cars runs fine otherwise, pulls nicely to higher RPMs and accellerates fine - once it got moving :-)

Any suggestions?

[Martin Greaves]

Try and put the f7 back in i think that the f11 make it a bit on the lean side.

[Sarge]

So, how did your car run BEFORE you had the carbs rebuilt?  Changing the idle jets three sizes leaner should produce something noticable!  I don't know your set-up, but on a 1776, I'd try something like 37mm vents, f7 tubes, 135 mains, 130-140 airs, and 60-65 idle fuels.  Also, make sure you have no vacumn leak.  The other thing that comes to mind is water in the fuel (from sitting over the winter months, condensation can cause problems...a little alchohol in the fuel tank will remedy this).  Hope this helps. 

[Andi/DFL]

car ran bad before the winter, but due to other problems, that are fixed now. main jet is 140, air ... uhm... yes, it has one :-) (need to write it down some day). So I will try the f7 tubes again. water in the tank... I will check that.

[Andi/DFL]

just another idea, that just came to my mind:
since a few weeks, I have a different pulley and adjusted the ignition to 7°. I think this could be not enough for the setup I use, maybe I should try 10-12°? Not enough advance can also be the cause for this kind of problem, I  think.

Maybe some of you can post their ignition timing, so I can get an idea in which direction I should go. I use a simple 009 w/points setup, will change to 010 soon.

[alex d]

what's your total advance? I would try 60 ot 65 idles as suggested anyway IMHO

[Andi/DFL]

what's your total advance?

acutally, I don't know. What is the total advance of a 009?

[besserwisser]

  You should have about 28-30 degrees advance total so depending on the 009 you could end up with 10-13 degrees at idle. I think 135-140 main  160-180 air and 55idle. Also make sure you have the right float level and that the fuelpreasure is on the money (3-3,5 psi)  The real solution is a third progressionhole but one can play with the idlesize to cure the bad switch between idle and low speed.Also check that you get enough from from youre accelerationpumps. God luck.

[Andi/DFL]

so I guess my jetting is ok, as it mainly matches everybody's suggestions and it proofed to be working in the past 2 years. I did not check the fuel pressure, I need to do that. The third progression holes have already been done and it was a remarkable change in driveability. I will try to correct the igniton tonight. Hope, this will help.

BTW: What chance do I have with an IDA to adjust how much fuel the accelerator pumps deliver? Is the only way to drill the jets (? the things that point down the venturi)?

[Sarge]

I agree with timing being a possible issue, too.  I like 32 degrees total advance.  Don't just set it staticly (engine off) at 10 degrees...use a strobe to make sure your getting full advance.  Also, don't forget to check and adjust yoiur point gap (46-48 degrees of dwell engine running) before setting the timing...then re-set the idle rpm.

[Rasser]

My guess would be either:

Bad points (bad points will give you exactly the problems you are talking about)
or Incorrect float height (to high float level and the mains will "come in" at higher rpms)...  try to just accelrate with the throttle 1/8 open and let it accelerate to 5000 rpm.

If it struggles at about 3000 rpm (2800-3200 is the normal transistion area where the main jets take over from the idlejets) then you should try to adjust your float height a little higher. Increasing the floatlevel will allow the mains to kick in at lower rpms (sooner).

oh, one last thing - never ever underestimate good synchronizing  ;-)

[Andi/DFL]

I checked the float setting when I bought the carbs in 2004. They were ok, according to a weber pdf, that I found. I will check that again. I've read somewhere, that you can check the float level, when you take out the main jet + tubes und measure the fuel level in the hole, is that correct? Would be a nice "quick 'n dirty" check :-)

I adjusted the ignition to 12° tonight, two seconds after that, my strobe light died... so I could not check the total advance, but I took it for a test ride and gues what: lesson learned. Always check the ignition first then check the carbs (I've read that a million times... :-) Runs good now right away from idle.

When accelerating with very little throttle, there is a very small "flat spot", just before the main jet comes in (it comes it at around 3500, tested that before with a very small main jet). Hardly recognizable, it's really small. That brings me back to checking the float level again. I probably should try the formerly used F7 tubes before. When the main jet starts working, everything is fine.

Thanks for the help everybody, now I hope for some good weather at the weekend to attend the Vollgas Kreuzers cruise night (when does it begin, guys?)

[Diederick/DVK]

You're shitting me Andi!
Are you coming over??

Well you're welcome at any time! Starts around 7pm
Send me a txt otherwise : +31-6-13154786

See you there sunbeam 

[Andi/DFL]

Are you coming over??

If the weather is right (I'm a real coward when it comes to weather). Would be a nice test drive, there are a lot of "tuning spots" on that part of the autobahn  to stop for some fine tuning on the way :-)

[Diederick/DVK]

Are you coming over??

If the weather is right (I'm a real coward when it comes to weather). Would be a nice test drive, there are a lot of "tuning spots" on that part of the autobahn  to stop for some fine tuning on the way :-)

Don't worry about the weather, the forecast looks good. A sunny 21 degrees 
But, i really should've wired up my monster by then... Mmh 

[Andi/DFL]

a small update:

it turned out, that one float was leaking. cylinder 1 was full of gas yesterday, as was my oil. sh*t! those floats are really BAD quality. replaced the floats, adjusted the carbs again and now it runs better than ever before. looks like the float was leaking just a little bit since I bought the carbs two years ago. If anyone knows some good, high quality replacement for the weber floats - let me know.

sorry, kreuzers. can't make it to the cruise night. my fuel money went into new oil and new floats :-(

[Diederick/DVK]

schade