Ford X-Flow 1760cc mis-fire Problem.

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John Carroll
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Ford X-Flow 1760cc mis-fire Problem.

Post by John Carroll » August 20th, 2006, 7:01 pm

Hello Guy, What a terrific site you have here, makes me want to go out and buy a Fiat or Lancia. I have heard of your expertise over here on the west coast of Canada.
I have a perplexing problem with a 1760cc Ford x-flow and was wondering if you could help. The engine is up and idling fine after a full rebuild and upgrade (stage 3 head-Cosworth A2 cam, bigger exhaust bundle, 40 dcoe's, bestek distributor etc.,)

The problem is when I come off idle, it starts to stutter around 2000rpm and will spit back through #2 cylinder. It feels as if the distributor is not advancing but testing shows it is. The Webers are second-hand but rebuilt I do know the main jet is a little small (115) but it should pick-up. I have rechecked everything (cam timing, ignition, carbs are balanced at idle.
Webers have Main 115
Emul. F16
Idle Jet 50F9
Air Corr. 160
Accl. Pump 35
Can you please help?
Regards, John.

Guy Croft
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Post by Guy Croft » August 21st, 2006, 8:05 am

John, hi

so what we have here is a pushrod '1800' running 40 DCOE with race head and L2 cam. The cam - from my Kent Cams data is a profile of about 8.8mm inlet ex lift, timed at 108 deg, so although the head is race prepped the cam is quite mild. I'll assume you've dialled in the cam correctly and the ignition timing is set say, 10 deg static advance.

Simple things first, I'd be running 34 chokes in the Weber 40s, these will give a good signal but still plenty of airflow on an 1800 unit with that mild cam. If yours are smaller go to 34mm and vice-versa.

As for the rest of the jetting:
Main jet 115 too small (lean) go to 135
emulsion tube F16 - OK
Idle jet 50F9 - OK
Air corrector 160 - too small (rich) - go to 175 or 180
Accelerator pump jet 35 - too small go to 45

Those new settings should be more-or less right and will certainly not cause the stutter on pick-up or damage the motor.

Fault-finding in order of simplicity in sequence of checks:

1. Test that the pump jets are working - with the engine 'off' look inside the carb barrels in turn with a torch, snap the throttle wide open, you should get a powerful laminar jet of fuel from each pump jet into the barrel. If you don't one or other of the pump jet pistons are sticking, the jets blocked, or the ball in one of the 2 pump jet bypass valves is seized (located in the bottom of the float chamber and prone to get stuck with calcium deposits).
At the same time make sure the cold start mechanism on the rear of the carbs is closed or it will make the motor very over-rich. You should start DCOE with several pumps on the throttle, they are very prone to flooding is the cold-start is used.

2. Test the resistance of the HT circuit and make sure you're not losing the spark at the plugs. If you don't have a resistance meter, crank the engine with one HT lead held 1cm from earth and crank - you should have a fat blue spark that jumps the gap easily. Better to test with the motor running and if you can find a Gunsons distributor via internet their little scissor-type HT spark test device is brilliant see:

http://82.165.33.164/product.asp?u=1581 ... &deptid=11

This is important though it probably is not the cause, I imagine everything in the ignition circuit is new, but many people will read this apart form you. The pressure in the cylinder goes up when you open the throttle and if the spark is losing energy thru old cabling etc it can die. Make sure at this stage that the problem is not simply plug fouling due to race plugs/over-rich idle mixture.

3. Start the motor and warm up at idle. Then:
a) Make sure fuel is not dripping into the carb barrels when running; this is a sign of carbs out of balance or float level too high/fuel pressure too high.
b) Check the ignition advance setting at idle (say 10 deg advance, no vaccum advance connected - if used).

4. Turn off the motor, take all the plugs out , isolate the ignition and ful supply, so a hot engine compression test. If you don't have a gauge, buy one. Snap-On is excellent but Sealey is also very good, sure there are many to choose from, but get one with a screw-in adaptor. You have not told me the CR - compression ratio - but not to worry, in general you're looking for cranking compression of well over 180psi.

More importantly we're looking for a bent valve causing the spitting, or blown head gasket. Unlikely but still need to so the checks and rule them out of the equation. If either of these is the fault, with a bit of luck it will show as low compression on one or more cylinders. It is important that the engine is fully warmed up because carbon fouling on the valves can show low compression, misfire at idle, but is soon scrubs off when the engine is driven.

5. I'd like to see details (good photo if possible, under 200 KB) of the exhaust header and silencers (mufflers). It is possible that the primary pipe configuration is wrong and causing pressure-wave interference between cylinders as you try to accelerate the motor, or there is high static pressure in the pipework ie: high back-pressure.

Alternatively you could begin perhaps by using a Gunson 'Colortune' - see same website above, to do a diagnostic check on the combustion with the engine warm. It is an excellent little tool. Things it would show up:
a) Good idle burn and mixture - royal blue flame
b) Too rich idle mixture or leaking pump jet - bright orange.
c) Good pump jet operation - changes instantly throttle is snapped open from royal blue to bright orange but stabilises back to royal blue if engine is settled back to idle.
d) No flame, just sparking - no fuel getting to cylinder - blocked idle jet or throttle closed on that carb.
e) Intermittent blue-orange flashing - head gasket or valve problem, or air leaking thru inlet manifold gasket and bypassing carb.


I hope this is useful. Print off and please check out these things and report back, OK?

GC

John Carroll
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Joined: August 16th, 2006, 12:02 am
Location: Victoria, B.C. Canada.
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Post by John Carroll » August 24th, 2006, 3:19 am

Hello Guy, Firstly thank you for the great reply. I had done most of your suggestions, but some I found most interesting. The first thing being the cam, it is an older A2 cosworth which has almost the same configuration as the Piper 285, I used this cam mainly because I believe it was developed for the small Fords, I could be dead wrong on that as most of my experience is with early Jags. I concentrated on the webers, finding that even after a rebuild they are entirely unsuitable, chokes are too small etc., I will rebuild them again to your suggested specs and see how things run. I did a compression check again and have 240-225 range, the 240 being on the cylinder that spit back. I then set the webers using a colourtune spark plug, no spitting back! but still won't accelerate. So off with the carbs and maybe the head just to be sure no bent valves. You have given me lots of food for thought and I will keep you informed of progress.
Just as a matter of interest, I was born in Liverpool in the 60's and raced modsports at Oulton Park.......a lifetime ago!
Regards, John.

Guy Croft
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Posts: 5031
Joined: June 18th, 2006, 9:31 am
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Post by Guy Croft » August 24th, 2006, 7:31 am

Good - that would now tend to narrow it down to wrong exhaust configuration or faulty pump jets.

GC

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