2.25 Petrol Weber Carb - Slow Start When Hot

[ricker]

Hi,

I have a 1970 2a with a 5 main 2.25 petrol motor and the 34ICH Weber carb. If I turn the motor off after warming it up and wait 10 to 20 minutes it takes about 10 seconds of spinning the starter to fire up. If I wait long enough for it to cool down somewhat it starts without hesitation. When cold it always starts without hesitation. The slow start only seems to occur when hot and sitting for a short while (like when I stop into a store to pick something up).

I think it is probably a fuel issue. Maybe vaporizing in the fuel line? I just bought some fuel line heat shield sleeve and will install that to see if it helps. Any other ideas would be greatly appreciated.

Thanks,

David

[knac1234]

David,

I have exactly the setup you have on my 72 SIII. Exactly the same problem/symptoms too. First time start when cold every time; first time start (maybe a few more cranks) when it's been sitting for a while but warm; wait sometimes a while to start it when hot and trying to restart shortly after. I THINK it is fuel vaporization. I have read-and asked the question-and I have heard that an electric fuel pump might help the issue if not eliminate it.

FWIW I have 4 Brit cars. Both the MGs, with electric fuel pumps, do not have this problem; the Imp and the Rover, with mechanical pumps, do have the identical issues. I have kicked around throwing an electric pump on both of them, but have yet to do it.

Julian

[martindktm]

I have the weber with mechanical pump and don't have that trouble. When hot I barely touch the key and it's already started.

[albersj51]

If it is, in fact, vapor lock, try the electric fuel pump combined with a bypass fuel filter near the carb. Gudjeon recommended this to me when mine would refuse to start for 20 minutes after sitting a moment in 95 degree summer heat. Of course, this was a while ago when my Rover was intact.

I believe the bypass filter he recommended was from a mid-80's Chrysler. I'll have to check it to get a P/N. When I did it, I took the blanking plate on my gas tank off, tapped it, and inserted a barb for the bypass hose to connect. From there I routed the hose to the bypass port on the filter. Very simple to do (even I could do it!).

However, confirm that it is vapor lock first. If you find that using fuel hose insulation works, let us know!

[mearstrae]

If going to an after market electric fuel pump be aware that most have an internal bypass and don't need a return line from the carb. However some of these may need a fuel pressure regulator, to keep down pressure at the carb.

'95 R.R. Classic LWB
'76 Series III Hybrid 109
'70 Rover 3500S

[ricker]

Hi Everyone,

Thanks for the replies.

Julian & mearstrae - I already have an electric fuel pump with in-line filters before and after it. I am not sure but I think it is the pump used on the Stage One trucks.

albersj51 - I am not familiar with a bypass fuel filter and don't know whether either of my filters are bypass or not. I would appreciate more info. Mine has never failed to start it just takes 5-10 seconds to start after warming up and then turned off for 10-20 minutes. After 45 minutes or so it fires right up.

Hopefully this weekend I will get the heat shield on the fuel line from the carb over the front of the engine down to where the mechanical pump used to be. I'll post the results.

Thanks again,

David

[martindktm]

How is the points/condensor/distributor/coil conditions?

I have also seen in the motorcycle and snowmobile world coil that would spark ok cold and when hot had a week spark. They where sparking the plugs with the plug out of the cylinder but could not do it under compression...

[bkreutz]

I have a hot restart problem, I'm not running a Weber but what's going on with mine is that the engine heat is making the fuel percolate over into the intake manifold flooding the engine, if I wait long enough the fuel evaporates but if I try to restart it after 10 or 20 minutes I push the accelerator pedal to the floor, leave it there and then crank the starter, fires right off. One of these days I'll try to fix it but I've gotten used to it and guess I'll wait until I have something else to repair. (don't want to rush into anything). HTH

[Tim Smith]

When it's hot and won't start, take the filter off and push the accelerator down. When you do that, watch to see that fuel gets squirted into the venturi by the accelerator pump. If that works then I'd start looking elsewhere. Like the spark.

Check the coil and see if it is very hot. When coils start to go, they will produce less spark as they warm up because they are breaking down either in the windings or the oil in them is breaking down or leaking out.

If you think you still have a fuel issue, then put a clear filter on at the carb. Something like a Fram G12 is cheap and easy enough to put inline. You will then be able to monitor the flow and see if it's boiling at any point.

[Tim Smith]

When it's hot and won't start, take the filter off and push the accelerator down. When you do that, watch to see that fuel gets squirted into the venturi by the accelerator pump. If that works then I'd start looking elsewhere. Like the spark.

Check the coil and see if it is very hot. When coils start to go, they will produce less spark as they warm up because they are breaking down either in the windings or the oil in them is breaking down or leaking out.

If you think you still have a fuel issue, then put a clear filter on at the carb. Something like a Fram G12 is cheap and easy enough to put inline. You will then be able to monitor the flow and see if it's boiling at any point.

[giftshopduane]

Most early sports cars that ran Webers (among others) have a hot start section in their owners manual. There is a long winded scientific explanation to this phenomenon that I won't pretend to understand or fill your head with lots of misinformation I will leave that up to you and Google or I can give you my brothers number, he and his wife can bore you to death with details.

When you try to start some carbureted systems it is necessary to perform it WOT thus increasing the AFR since a hot engine requires less fuel and more air to combust than a cold motor. (again I went to art school my brother was the scientist, therefore I can't give an accurate explanation of why, but I have spent countless hours repairing, rebuilding and synchronizing multiple carb'd Italian V12's)

Now if your experiencing percolation due to heat soak then you should try a phenolic spacer under your carb as an insulator if there already isn't one.

If your are running or have want to run an electric fuel pump then please resist using a pulse type fuel pump (Mr Gaasket, Powerflow, Pierburg or the cheap inline style from NAPA etc...) go with a Carter Rotary vane. They are far superior, quiet (ish) I like the GP4070, Summit sells it. I have had very good luck with these, they run at 6psi which is plenty for a carb, you'll need over 8 to push past the needle valve and flood it, I think they are spec'd between 4 and 6psi. They flow well, last long. I find that the pulse type can foul easily, and when they fail they tend to suck air and lean the mix rather than just failing like the rotary vane pump. Just make sure the connectors are push on completely and seat firmly to the terminals on the pump, someday you'll be scratching your head why the pump failed when it's just the connector vibrated off the terminal.

Also find the need to junk your points, pick up a Pertronix for your distibutor, well worth the $$, takes an antiquated design out of the equation. This is not to say that some are running points with great success, millions have been doing so, I just think it makes life with a distributor much nicer. Tip: keep a good set of points in your kit, I'm not saying Pertronix aren't failsafe, points generally are, they just don't fire off the motor as easily.

[cgalpin]

I have this exact same problem with my '63 IIA with weber 34ICH and stock (or at least stock style) mechanical fuel pump with sediment bowl. I have a clear filter so just looked and sure enough, instead of the usual near half full, it is basically empty (say 1/4 max) after sitting for a while after a drive. Does this mean it's the fuel vaporizing, and is the recommended solution insulating the fuel line?

[yorker]

H
I am not familiar with a bypass fuel filter and don't know whether either of my filters are bypass or not. I would appreciate more info. Mine has never failed to start it just takes 5-10 seconds to start after warming up and then turned off for 10-20 minutes. After 45 minutes or so it fires right up.

It is a filter with three places to put a fuel line, one of which you run back to the tank. Thatt way you get a constant supply of cool fuel from the tank in the fuel lines. They look like this:


(I think the Fram G5387 is the #?)

[giftshopduane]

I have this exact same problem with my '63 IIA with weber 34ICH and stock (or at least stock style) mechanical fuel pump with sediment bowl. I have a clear filter so just looked and sure enough, instead of the usual near half full, it is basically empty (say 1/4 max) after sitting for a while after a drive. Does this mean it's the fuel vaporizing, and is the recommended solution insulating the fuel line?

I would bet your weeping fuel back through the pump. I won't assume the hose being used but I am going to guess at 3/8" which has a sizable wall thickness providing decent insulation. I would still lean towards something else in the system is amiss. I haven't seen an insulated fuel line in practice, at least not used to combat vapor lock, usually to insulate from close proximity to the exhaust manifold.

My 79' F250 runs a factory hard line from the pump alongside the block under the water pump and it doesn't exhibit any issues due to heat, I will venture a guess that my 460ci runs hotter than a series motor. The only time I have seen a heat issue affecting the fuel stability was with a 427 Cobra, which ran inherently super hot, no under hood ventilation, 0 mile tight motor, inproperly tuned and jetted. I added a carb spacer, got the timing and jetting right and never had an issue.

Hot start is pretty common, if it starts WOT I'm ok with that, as long as it runs and op's fine once started, but I will assume that all of the millions of Series produced don't experience this problem therefore you have something else at play here. Make sure all the other systems are spot on, valves adjusted, compression good, leads and grounds clean and healthy, plugs, check, fuel pump solid, tank's clean etc... if all else checks out then what else is there?

I have seen modern fuel injected cars need a bit of gas pedal to get them to start when hot.

[cgalpin]

I would bet your weeping fuel back through the pump. I won't assume the hose being used but I am going to guess at 3/8" which has a sizable wall thickness providing decent insulation. I would still lean towards something else in the system is amiss. I haven't seen an insulated fuel line in practice, at least not used to combat vapor lock, usually to insulate from close proximity to the exhaust manifold.

I have a hard plastic line up to the filter - looks to be smaller than 3/8", so maybe 1/4". If the fuel was draining back (which seems like a very reasonable bet to me), what makes it ok after sitting long enough for everything to cool? That's the part that is baffling - you would think once drained it wouldn't come back.

Hot start is pretty common, if it starts WOT I'm ok with that, as long as it runs and op's fine once started, but I will assume that all of the millions of Series produced don't experience this problem therefore you have something else at play here. Make sure all the other systems are spot on, valves adjusted, compression good, leads and grounds clean and healthy, plugs, check, fuel pump solid, tank's clean etc... if all else checks out then what else is there?

I have seen modern fuel injected cars need a bit of gas pedal to get them to start when hot.

I will try WOT next chance I get and pay attention to the fuel level at cold start as well as after short stop and longer stops. I have had other fuel related issue which I'll describe, but am not sure of they are related. Almost randomly my truck will alternate from running perfectly to having zero power without the choke pulled all the way out. Sometimes it can alternate between states multiple times in the same trip, and sometimes it says good or bad for extended periods. I noticed it went from good to bad the other day after hitting a bump which might be an indicator of junk in the fuel clogging things up. It seems to run fine otherwise and idles great. I adjusted the valves yesterday but they were at 0.011 before which I think is acceptable.

The good/bad thing is my truck is running great right now so none of these symptoms are present. It's hard to say things are a problem when they are not causing the problem at the current time. I noticed some junk in the fuel pump sediment bowl yesterday so cleaned it out. I went to see if the fuel pickup was clean but when I pulled the access cover the hole where the line goes into the tank looked smaller than I expected to see so decided to leave it for now since the problem is gone for now and I didn't want to rock the boat. I'll check the green bible so I know what to expect next time. Here is what the gunk looked like. It almost had an alligator skin pattern on the on the yellow (rubber?) almost like what you'd see on dish washing gloves. Maybe I should look in the tank



Sorry if this is getting to be a hijack.

Thanks,
charles