Hi all,

I've recently reassembled my datsun 1200 gx motor in my spitfire mk1. I'm running SU's (2x 1 1/2"). Prior to stripping the car down for nut and bolt resto it was running fine.

Now... since getting everything back together there have been a few modifications external to the motor.

Firstly I've put on an electric fuel pump with a pressure regulator.

Secondly I've fit a programmable high energy ignition system.

Thirdly I've built and fit a large bore free flowing exhaust.

The problem:

I can get a decent idle smooth at 800rpm. Anything lower than this and it splutters horribly.

If I try and rev it it backfires horribly out the carb mouth - repeatedly so - and I can't rev it beyond about 1800RPM. With the throttle butterfly linkages undone I can try and rev each carb individually and they both do the same thing.

With the vacuum advance plugged and the motor idling at 800rpm I have it set to 10deg BTDC.

I've noticed that the advance moves to about 20deg BTDC at the max revs I can get i.e. sub 2000RPM.

Over the past 4 weeks of frustration I've stripped and reassembled the carbs - noting lots of crud in the float bowls and since cleaning everything with compressed air. This made no difference.

Observations

The pistons are not sticking.

The butterflies are closing properly - i.e. I can stall the motor if I wind each screw back out.

I am surprised that I can't get a smoother low idle. I used to be able to do as low as 500rpm prior to stripping the car down for the restoration.

I've checked float bowl heights and all is good (baring in mind that they weren't changed from when it used to run fine).

I have fuel at each jet.

I tried heavier piston damping springs and this made no difference.

I tried no piston damping springs at all .... no difference.

The pistons do rise when I try and rev it but they drop just after the backfire out the carb and then repeat the process of rise backfire rise backfire....

even after extended periods of what seems like a good idle the plugs are black and there's fuel up around the threads.

I've checked for vacuum leaks and haven't found anything.

Present conclusions / thoughts

I'm starting to lean towards the ignition side of things. Perhaps it's advancing too quickly. Could this cause induction backfires?
From my reading an induction backfire is usually caused by a temporary lean condition.

Perhaps the fuel pressure is too great and it's pushing by the floats and surging the carbs - this sounds unlikely as I can get a smooth idle at 800rpm - although I have noted it hunts up and down if I try an idle below the 800rpm mark.

As always with cars like this the obvious thing to blame was the carbs but honestly given that I've only changed ignition and fuel pump it has to be one of those things.

This is really giving me the craps.

Any advice would be much appreciated.

first of all I had a 76 spitfire , they are fun to drive , very low to the ground. sounds like it is in the ign. to me but you said the plugs had fuel on them , cause the backfire sounds like a high ign. timming. did you go as far as a timing chain & gears? just wondering about the timing.You could have multiple probs.

Thanks for your reply.

This restorationhas taken 2.5 years so far. I rebuilt the motor and had it running well before I stripped down the body. So basically I had a #### car with the new motor in it just to test it. That was 12 months ago. It worked just fine. Then I took the motor out and put it on a stand did the body work and dropped the motor back in. At the same time as the body work I did the electric fuel pump, the new exhaust, and the programmable ignition.

I'll try and get the enthusiasm and courage up to go and reprogram the ignition system. If I have no luck there I'll drop in the original dissy and see if it runs on bog standard ignition.

I think all the heavy backfiring was a chance for fuel to go everywhere i.e. puff back out the carbs as well as flood the motor temp (hence the backfire perhaps). So the fuel around the plug threads could still be related.

Hi All,

It lives

I'm really not sure what's going on here but I'll detail solution.

I figured it was ignition - advancing too fast.

My programmable ignition has two advance curves which I can switch between on the fly. So I switched to mode 2 and then reprogrammed it just by guessing some conservative numbers i.e. 2deg vac advance rather than 10ged, slower ramp up, and started the ramp later.

Surprisingly the car fired first turn of the key - revved just fine - blipped around to 5.5kRPM very easy.

Curiousity had me at this stage so I switched back to the original advance settings (i.e. curve 1) and this works just fine too.

I'm guessing either a gremlin got in the garage during the week and fixed it - or there was a bum setting in the eprom of the advance module that got fixed when I programmed in the second curve.

i think the problem is the car, maybe the datsun engine dont like to be inside a inglish car.

Hey britishcarfreak,

I'm a Triumph fan from way back - My 1st car was a 2500 TC.
Love what you've done w/ the spitfire..... It certainly seems as though you've put your fair share of blood sweat & tears into that one & it's starting to pay off.

I'm involved in a 1200 ute project at the moment, but I've always wondered about doing something wicked to a TR4. ie/ Late model 16 valve motor...... 4age or similar. Not sure what else would fit?

Have you seen anything like this around the traps?

I'll put my hand up here too- my first car was a dolomite sprint. great fun but slightly sketchy handling. one guy had replaced the 2l sprint engine with a 4age.... which seems kind of ridiculous since the 16v engine was always the most impressive thing about the sprint (except for its lack of reliability!!) but those inline sixes really didn't have much going for them so the sooner you can slot in a RB25 the better I reckon....... (unless tr4's were 4 bangers in which case the sr20 would be sweet- I only have experience with tr6's)..... you might even be able to graft a nissan rear end into it and replace that dodgy triumph setup.

well off topic- sorry

Yes perhaps the motor is unhappy about its alternate sports car body. Personally I think it should be proud to be housed in its slick new body

Now for 2500's yes they are hell boring in standard form but I've got a heavily modified one and it's seriously fun. It gives plenty of new cars a run for their money.

The spitfire has been a total bitch to get together but it's starting to look worth it. I'm really curious to know how the GX motor will get along.

Coops: The TR4 became the TR5 later on and hence it is certainly big enough to take the triumph 6 cyl motor. Thus I would imagine that almost anything would fit in there as long as it's not too wide. (given that the triumph 6 cyl is reallly very large for its small capacity (block is bloody heavy and too thick))

One of my buddies has a dolly sprint in modified form (with standard motor) and it is often off the road for fixes but very nice when running.

Yes you can certianly do conversions for nissan rear ends (or subaru).