other Fuel Boiling in Carb

['76mintgrün'02]

There is a station near my house with 87 octane ethanol free.

92 octane ethanol blend or 87 pure, which would you choose?

Edited July 15, 2015 by '76Mintgrun'02

[zinz]

Hands down....I'd MUCH rather add octane booster (if I needed it) than run ethanol in my car.  It's so terrible on fuel systems, aluminum engine parts, seals, etc... Not to mention, Ethanol has SIGNIFICANTLY lower heat value (Btu/lb) meaning you need to burn more of it to produce the same amount of work....ie: lower fuel mileage as compared to pure gas.  Checking my mileage notes here...driving to MidAm this year?  I got 23.67mpg on my last stop with ethanol-added fuel, then the next stop after filling up with pure gas, I got 27.76 mpg... running pretty hard on the highway and some mountain blasting in northeast OK.  That's a no-brainer, to me.

 

If you have a stock engine, the 87 octane will likely run without hiccup.  Easy way to find out. Fill the tank, bring the engine to operating temps, find a steep hill and run up it in 3rd gear... If you hear any pinging, then you know your car needs more octane.  Also try a plug-chop to confirm.

 

This is obviously, a  hot-button issue for me... ethanol subsidies are a scourge.  

 

Ed

[TobyB]

I like Jimk's solution- just Megasquirt it and be done!

 

(heh heh heh)

 

t

['76mintgrün'02]

You're like one of the '123 guys' that butt-in on the distributor rebuild threads... or maybe megajolt?

 

Don't you miss the nostalgia?

[Nuthatch]

Many have grappled with this problem, myself included. 1976 2002, Metric Mechanic 2200 Sport motor, Weber 40/40 DFAV. 

 

Ethanol (another term for pure grain alcohol) lowers the boiling point of fuel markedly, and that led to real trouble for me. Fuel makes its way in relatively cool conditions from the tank to the firewall, but once it enters the engine compartment, it has all sorts of time to grow quite warm during the slow journey to the carb. After a good run in any season, and after shutdown of the motor, residual heat atop gathering atop my car's intake manifold would cause the already-hot fuel to boil audibly in the bowl and percolate right into the throat of the carb (which lacks an anti-percolation feature). This resulted in worrisome levels of fumes, and caused a super-rich flooding condition that made it hard to restart the car when hot. I saw no evidence that this problem was due to actual engine overheating: the gauge was right in the familiar sweet spot (with brand new sender), and when measured with an infrared thermometer after warmup, the radiator, block, and manifold temperatures seemed entirely fine. Driving performance was great. The troublesome issues arose only after the engine was turned off. Opening the hood wide to dissipate heat after stopping improved things to be sure, but that’s no way to live.

 

I tried all the standard remedies: installed a spacer block under the carb, insulated the fuel lines and pump, insulated the carb bowl, replaced the needle and seat, tweaked the fuel level in the bowl by adjusting the float. One BMW expert suggested a fuel pressure regulator between fuel pump and carb, dialed down to 2.5 PSI. Alas, none of this brought any improvement whatever. All the local gurus were stumped, and I was starting to run out of ideas. One far-out tactic did come to my attention: as noted in a post above, some have reported that they've cured this very problem by installing a timed fan positioned to blow air over the carb for 15 minutes after shutdown. That seemed like an unduly complicated workaround, one I was not eager to adopt.

 

Then came a final inspiration. As part of the emission-control package installed in US models for the 1976 production year, my car was originally set up with a return line that sent fuel back to the tank: just enough went to the carb, with the rest heading back to the tank via a diverter fitting. This return loop had been disconnected many years ago, when the belt-driven air pump (remember those?) and other associated gear was removed. 

 

My new thought was as follows: if I could keep cool fuel circulating, it wouldn’t have a chance to heat up while sitting in the line moving gradually across the hot engine. I located the old hard return line that runs under the driver’s side of the car. The old soft line from the tank to the hard line was completely deteriorated, but was not difficult to replace. The forward end of the hard line ends up just under the steering box, and it was easy to make a new connection there. I then inserted a 5/16″ (8mm) tee downstream from the pump and just before the intake fitting on the carb. Some fuel goes to the carb, the rest back to the tank. This means that fuel now circulates continuously and has no chance to pick up heat while sitting in the engine bay. The only “hot” segment of fuel line is the very short portion between tee and carb, and that brief run simply doesn’t afford the fuel sufficient time to warm appreciably. Yes, the carb bowl may be as warm as ever after shutdown, but when the now-cooler fuel reaches it, it no longer boils. 

 

This fix brought a complete end to the unfortunate symptoms.

[rstclark]

Has anyone tried a fuel pressure regulator with or without the spacer ?

Holly makes a low pressure regulator that works for 1 - 4 lbs.

['76mintgrün'02]

I tried all the standard remedies: installed a spacer block under the carb, insulated the fuel lines and pump, insulated the carb bowl, replaced the needle and seat, tweaked the fuel level in the bowl by adjusting the float. One BMW expert suggested a fuel pressure regulator between fuel pump and carb, dialed down to 2.5 PSI. Alas, none of this brought any improvement whatever.

 

 

 

I installed a Jeep fuel filter between the pump and Weber.

The filter has two lines coming out, one to the carb and the other has a pressure bypass valve, which, in theory, sends that fuel back to the tank; using the fuel return line mentioned in the post above.

 

Link to filter info http://www.bmw2002faq.com/topic/118831-flooding-and-hot-start/

 

 

It seemed to help in my situation.

[TobyB]

I had missed that filter in the earlier post- that's brilliant! 

 

I found (with a different, non- crossflow engine) that the

bypass system really DOES work most of the time.  On that

engine, I used a very small restrictor in the return, and the carbs (SU's)

were very happy with that.

 

I would bet, reading the other thread, that the extra port is simply open (thus the 'clocking' requirement)

and that a small restrictor (1/16" or so) might be  a good idea here, too.  Otherwise, going up a hill,

you'll tend to lose flow to the carb as the return starts to siphon fuel out of the filter.

 

Figured that one out the hard way...

 

t

[Nuthatch]

Excellent post from '76Mintgrun'02, and nice photo. I'd heard about the Jeep filter idea, and understand that this has worked for a number of folks. As long as sufficient fuel pressure to the carb can be maintained in all driving conditions, you're good to zoom. 

 

As to the overall problem of fuel boiling, all three Webers commonly used in 2002s seem to be susceptible to this problem: 32/36, 38/38 (especially sensitive, it seems),  and 40/40. Back in the day, no one experienced these difficulties. Without doubt, ethanol has to be the cause. 

 

There are about a dozen stations in Massachusetts that sell ethanol-free fuel, but unfortunately none are close to me. A state-by-state guide to availability can be found here: 

 

http://pure-gas.org

['76mintgrün'02]

Since that photo above was taken, I have 'clocked' my filter, so the bypass outlet is at the twelve o'clock position, as the earlier thread suggested. 

 

I also added a piece of radiator hose to the filter, to act as a cushion, since it tends to sit on the alternator.

 

 

While messing with  my fuel pump, I put a pressure gauge on both outlets of the filter and I got about four psi on each.  I would like to do that test again though.  I cannot remember if I plugged the main outlet to get a reading on the bypass outlet....

 

If I remember correctly, I tried to blow through the filter when I first got it and air only went through the middle fitting, implying that the other, smaller one, did in fact have some sort of valve.  

 

(I have never had any fuel starvation issues with this set up).

Edited July 20, 2015 by '76Mintgrun'02

[zinz]

The Jeep filter seems to be a winner!  I'll have to incorporate one of those into the '75... Perfect timing, too!  The next project was to swap out the tired, leaking, 32/36 with water choke, for a known-good 32/36 with 'lectric choke that I have on the shelf.  The '75 appears to have the return line tucked away in the bowels of the engine bay.  I'll confirm and get new hoses, as needed.

 

Great solution, Tom.  And it doesn't cost an arm and a leg!  We are expecting 100 degree days for the next month, so this will be put to the torture test... Stay tuned!

 

Ed Z

['76mintgrün'02]

I think it is a great solution, but I cannot take credit for it... I posted one or two of the links I had found back when I put one in.

It looks like it was originally Pat Allen who came up with it... maybe?

 

I have mentioned these two concerns before, but will put them here again:

 

If you are sending fuel back to the tank, make sure the vent line is not plugged.  Mine had a screw in it and would not allow the pressure to escape.  I had very strong fuel smell and a woosh of air when I opened the tank.  That could have been a mess!  Removing that little screw solved the problem.

 

Another thing to check is the steel return line, where it runs by the pedal box.  I picked at a rusty spot on mine and fuel came out.  I simply cut that section out and replaced it with rubber.  Once again, that could have been a mess, but I got lucky.

[zinz]

good deal.  I'll be sure to check all that as I progress...

 

I know full-well that this 32/36 will percolate... It's the carb I removed from my '71 when I put the Solex side drafts on.  I'm interested to see if it solves the problem!

Ed