is my carb undersized for 2F?

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hi sarge,
thanks so much!!
i got your pm and will call but it may be a few days as i have to tend to my day job first.
plus, i want to check a few things before we talk:
1) my float level - my 32/36 has a plastic float, and i presume that per your drawing above, 51 should be 18mm as that's what the weber directions say should be the deflection. if it's not, how is the float level actually adjusted? by bending the tab?
2) my vacuum advance seems to work properly, but i think my dizzy also has a centrifugal advance, as when i disconnect the vacuum adv, the timing will still advance under acceleration. maybe it is advancing too far?!?! my dizzy does have an octane adjuster on the left side and per my book, it's supposed to change the timing slightly depending upon what octane gas it's running. i've tried to set it at zero. also, per my book, i may go ahead and pull the dizzy as it now seems really suspect and may be malfunctioning, which could be a large part of my back fire issues.

in trying to make it run right, and per a guy with redline telling me that my carb's too lean, i'm the one (or the dummy) whose been putting all those different jets in the carb, although i've not changed the emulsion tubes; those are original and both #F50. you're correct, the plugs are blackened and do have soot deposits on them.
talk soon and thanks again!!!
 
There are two tabs for adjusting the float - one rides on the float valve itself and the other bottoms against the outside of the valve assembly to limit drop . I usually set the top height first (fuel level in bowl) and then set the drop to around 4-5mm of travel at the valve itself . Those nitrofil floats are nice but the frames can be tweaked badly - from the factory stamping in Spain . Italian units never used that float , brass only and their frames were more consistent .
Hence, you have to take the settings with a grain of salt since there is no window to verify fuel level . Sometimes it's best to set it to factory spec and test the carb - if there is an issue you adjust it up or down a few mm to see if makes a positive improvement .

What do you have for a fuel system at this time ? The return line is very important - due to the design of the Weber's float valve and float frame there isn't a lot of leverage against that needle valve by design - this is why they recommend 3psi . Unless it's a high-performance engine I'd recommend using a return line in 8mm or 5/16" , 1/4" is also acceptable . Without a return you'll fight with it's fuel pressure issues . Regulators make this issue worse as they are a variable and not consistent enough for tests .

Get rid of those big jets , your washing down the cylinder walls/rings and can damage the engine quickly . 150 should be the biggest main jet , with your compression numbers I'd say 140-145 is more likely .

I'll be gone tomorrow most of the day and Wednesday may be out as well . After that , all is good .
Sarge
 
Weber Sarge said:
There are two tabs for adjusting the float - one rides on the float valve itself and the other bottoms against the outside of the valve assembly to limit drop . I usually set the top height first (fuel level in bowl) and then set the drop to around 4-5mm of travel at the valve itself . Those nitrofil floats are nice but the frames can be tweaked badly - from the factory stamping in Spain . Italian units never used that float , brass only and their frames were more consistent .
Hence, you have to take the settings with a grain of salt since there is no window to verify fuel level . Sometimes it's best to set it to factory spec and test the carb - if there is an issue you adjust it up or down a few mm to see if makes a positive improvement .

What do you have for a fuel system at this time ? The return line is very important - due to the design of the Weber's float valve and float frame there isn't a lot of leverage against that needle valve by design - this is why they recommend 3psi . Unless it's a high-performance engine I'd recommend using a return line in 8mm or 5/16" , 1/4" is also acceptable . Without a return you'll fight with it's fuel pressure issues . Regulators make this issue worse as they are a variable and not consistent enough for tests .

Get rid of those big jets , your washing down the cylinder walls/rings and can damage the engine quickly . 150 should be the biggest main jet , with your compression numbers I'd say 140-145 is more likely .

I'll be gone tomorrow most of the day and Wednesday may be out as well . After that , all is good .
Sarge
Click to expand...


That is some great info. Thanks
 
unfortunately, i've had to work lately to support my cruiser's unending thirsty habit(s), but here's an update of what else i've most recently done:

1) removed the fuel regulator
2) installed a cj fuel filter downstream of my electric fuel pump (between pump and carb) with a return line (currently just have a length of fuel line stuck into the gas tank for excess fuel from the filter)
3) adjusted the 32/36's float per sarge's diagram and instruction (good info too!!!!!)

with the above done, my f eng still backfires at all throttle positions upon sudden acceleration - i really have to watch my eyebrows. at idle, the vacuum is reading about 14" with some fluctuation; upon sudden acceleration, it drops to 0" and backfires thru the carb. upon reasonably slow but steady acceleration, the engine revs very well, to 3000 rpm, and the vacuum increases to about 17".
i have played with the ignition timing, and when it's advanced so much that the mark doesn't appear in the window at all, not even at slow idle (525 rpm), the engine does run better (that is, it does not backfire through the carb) but it then has a "hesitation" upon acceleration - it's prob too far advanced. this morning i plan to pull the distributor for inspection and disassembly if necessary, but right now i do not think it's condition is an issue, but we shall see....
 
I'd bet that distributor is at least half the issue - other half is fuel delivery system . Use the stock mechanical pump and ditch that electric asap - they do not provide a steady flow/pressure like the OEM unit .
Pay close attention to your hard fuel lines on the frame , I initially had mine backwards and it ran great with the tank full , hit's 3/4 mark and wouldn't pump fuel - duh . After tracing the lines from the tank it was obvious - I had hooked up the tank's return line to the fuel pump , just like the PO ....

Sarge
 
I am not familiar with that particular Weber carb, but it should have an accelerator pump. Is it working? You should see fuel squirt into the bore when you open the throttle. Backfiring through the carb is a classic sign of lean air/fuel mix that is too lean to ignite by spark.
 
Well, this is getting really frustrating, totally exasperating... Pulled the distributor yesterday, it looks very new, definitely Toyota as it still has the tag, no slack in bushings, very little gear wear, vacuum advance works perfectly with no diaphragm leaks or issues.. The distributor appears to be in perfect order. We have a test stand to work on solid state ign systems for industrial engines and I am now confident that the dizzy is not a cause for my engine's problems. We then bypassed the electric and hooked up the mechanical fuel pump, fuel flow and pressure are about the same. My gas tank is not, and never appears to have been equipped with a return fuel line, but it does have a vent line from the top of the tank going up to near the top of the filler neck by the cap. I can tee a return line into that vent when the time comes but for now that I know is not an issue. Anyway, I cranked the engine and no change - still backfiring through the carb :-((((
as for your suggestion pin_head, thanks, but i have checked for fuel being
injected into the throat upon rapid acceleration and it appears that the accelerator pump is working correctly, as it looks to be an ample amount of fuel squirting out of the jet.
 
Ok , at this point the only thing that can cause the issue is the transitional circuit holes in the carb or the throttle plates are totally out of whack . Without a return line it's going to be difficult to set up a return due to tank design - you cannot use the vent line system as it will pressurize the tank and make things worse .

If there is no sign of fuel dripping at a base idle then it's safe to assume the needle is holding the pressure for the time being .

Now, in your description you say "upon rapid acceleration" it backfires through the carb . Are you literally snapping the throttle open - ie: drag launch , or just opening it quickly as "trying to get ahead of traffic " ? It's tough to diagnose issues without seeing firsthand how things react in person , so just trying to nail things down a bit more .

If the distributor is showing good advance with the engine running - as in moving the timing mark around 18-20* upon opening of the throttle and inducing vacuum off the timed port to the advance , that is fine for now . The main concerns with the distributor is that it consistently returns to a base point and moves the advance the same every time - then all is good there .

If the carb is indeed plugged up , I can walk you through how to properly clean it with compressed air and brake cleaner . There are things that you have to be careful with , especially the special o-rings at the idle jet holders as they are hard to source and not an off-the-shelf part .

If it comes down to no results you could send it here and I'll check it over and test it .
Sarge
 
Lack of transition fuel would make sense if it only did it off idle, but since he says it will do the same thing when you nail if when cruising at any speed, the throttle has to be open and the transition fuel all in when you are cruising above 25MPH.

I'm thinking that he has a large vacuum leak that he hasn't found yet (bottom of intake crack; brake booster; PCV; etc) and that he is compensating for this by increasing the idle speed so that it idles off the main nozzles. Take a peek at idle and see if you can see fuel coming out of the main nozzles. The other clue is that you can shut off the idle mix screw and there is no effect.
 
Having been down the vacuum leak road I totally agree. You need to measure your vacuum as you adjust the carb off the inflated idle settings, if the vac drops off the cliff as you come down to 600-650 rpm you have another problem to hunt down. A year ago I was convinced I had a carb issue before I found out I was leaking like crazy at the manifold (due to headers that were not the same flange depth as the intake flanges), only took me 3 strips down to the head before I abandoned all the bs with trying different gaskets (and multiples thereof) and measured and fixed the cause of my problem. Make darn sure you have manifold vacuum at idle speeds, otherwise you will try different solutions for ever without solving your real problem. I know you've received some good input from WS and others on your carb, just make sure you don't have a leak.
 
at this point, i'm really thinking my f engine has to have a bad valve or two, and here's why:

i know the ignition system is good.
fuel quality and fuel delivery system is good.
i have checked for vacuum leaks extensively: with a bench tach and vac gauge connected, engine idling at 400 rpm, and again the same test idling at 525 rpm, i sprayed starting fluid around all manifold connections, around the entire manifold, and around the entire carb - of course, starting fluid is nothing but pure ether and is extremely flammable so i was VERY CAREFUL and cautious!!! and i do NOT recommend this! nevertheless, i have no vacuum leak(s) - the only area(s) i see any change in rpm or vac while doing the test is at the carb throttle shaft.

i pulled the weber and reinstalled the holley 500 that was on it when i bought her (i had previously put a rebuild kit in it) and checked for vacuum leaks exactly as i'd done above with the weber: she idles much smoother than with the weber - at 525 rpm, vac is 13", at 400 rpm, vac = 11". ok, that's good. slowly increasing rpm up to and through 2500, vac increases to 17" or so and holds fairly steady. that's good too. BUT! when i rapidly open the throttle, as i'd do to take off fast from a standing start, she backfires through the carb. the key here i think, is that when she backfires, a pretty large amount of fuel is also blown out of the airhorn, and it sometimes ignites with a flame a foot or so high...it'd be cool as a dragster or for cooking, but not too cool for my f engine. it's obviously not a lean backfire or else it wouldn't be spitting out so much fuel, and the only source for ignition has to be from the spark/combustion inside a cylinder and back through a leaking valve.. hence, there has to be a valve that's not closing, and thus probably burned, and so fairly soon, the head WILL be coming off... Grrrrrr....

thanks again to everyone whose trying to help me with this dilemma!!!!!
it will be a week or so before i know anything (day job), i will post what i find as soon as i can.
 
thanks sarge, i enjoyed it too!
i'll be looking forward to seeing your carb mods and the venting system you've developed. once i've rebuilt the head, and hopefully that's all i have to do to it, for performance, economy, etc, i'll probably go back to the weber and will definitely be doing your modification.
it's in the high 70's here, too warm for december, lots of mosquitoes will be in our future, but great weather to enjoy!
 
FJ40Jim said:
without re-reading the whole thread....
What do the compression numbers show?
Click to expand...

Jim-
Compression is not great but it's enough to where it should run ok. I don't have my notes right now but they're between about 102 to 122; all cylinders increase about 10# with a shot of oil.
I presume with rings, etc in good shape they should be about 150 but I have no specs on it.
 
That's what we'll be doing... Problem is, once I pull the head, I'm about 1/6 or so done with just going ahead with a major... Does SOR sell decent overhaul kits? I'd probably run a chrome ring, shave the head a little, etc...
 
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