Fiat 130TC misfire problem

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dafnos

Fiat 130TC misfire problem

Post by dafnos » July 2nd, 2006, 9:07 pm

i have a strada abarth 130 tc with some mods(weber45dcoe's,cams,hc pistons,polished and ported head) but the car seems to chocked when i try to accellerate from low rpm in full throttle,but if the engine run from 3000rpm and up seems ok! the ignition is a digiplex from a Lancia delta gt 1600 the original is burned and i never drove the car with it's original ignition.i thing maybe it's ig.timing problem.the ignition timing it's not affected when i turn tthe distributor in advance or retard.is tha normal? or work only on hi.rpm? what you suggest? (if you thing it's carb problem give me some standards to start from they work on 155 main jets 200 air corrector(155,210) f16 emulsion tubes 45 idle jets and 45 accel jets. nice job with the site!!! with regards dafnos

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Post by F138 » July 3rd, 2006, 7:49 am

I got the same problem with my engine too. Nearly the same specs but original 130TC ignition. When I throttle full with lower revs than 2800, the engine stalls (is the the right word?). Terrible feeling. This appeared when I changed from Solex40 to Weber45.

My carb jetting: Weber 45DCOE152 , 36mm chokes, 55F8 idle, air corretor 180, emulsion tube F16, main jet 138.

So I think it got nothing to do with your ignition but with the 45s, the mixture is getting too lean during heavy accelerating at low revs. I read something in an original Weber workshop manual about other emulsion tubes (F7?) which can eliminate the problem. Another experienced guy told me to use bigger idle jets. I will have to do some experiments....

But as I loved my "old" torque engine which could accelerate the car at every situation, I just bought some 40DCOEs to downgrade and getting the old behaviour back. But it looked good at the dyno, when I had 139,6 HP at the stock engine only by changing carbs....

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Post by Guy Croft » July 3rd, 2006, 10:12 am

Hi guys

well, I'd say that's not symptomatic of a carb jetting problem per se, both engines should run quite/very well with your settings:

F138, your want maybe to go up from 138 to 145 main, but F16 emulsion tube is definitely OK.
Dafnos - Jetting-wise, I'd need to know the cams before being more certain but maybe go to 145 main and air corrector from to 175-180

Because you have both identified 'hesistation' I'd maybe be looking for a problem with:
1. Accelerative enrichment issue - pump jets not working properly
2. Low fuel delivery to the carbs - pump/filter

A very sharp-sudden loss of power that throws you forward in your seat under acceleration is certainly loss of ignition, hesitation under acceleration especially trying to drive thru those speeds you've mentioned is usually fuel or high exhaust back pressure, although intermittent spark (misfire) or weak spark can do that too.

You could be losing spark energy if on old HT leads, you could both well have an exhaust system back pressure problem - the new cams if any good may not be able to flow thru the silencer systems esp if OE 130TC (and old).

The 130TC ignition timing is electronic and the base static setting is controlled from the front pulley sensor, not the distributor. The sensor must be exactly opposite the lug on the crank front pulley at tdc and 0.4 - 0.5mm from it. See photos at

http://guy-croft.com/viewtopic.php?t=87

GC

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Post by Julian » July 3rd, 2006, 11:00 am

One small note - if the distributor is not set correctly it is possible for the spark to weaken, fail or the wrong cylinder to fire under extreme conditions. Unlike later coilpack or coil-on-plug ignition systems you are still reliant on the rotor arm being in the tight place to transmit the discharge to the right lead/plug.

If you've been fiddling and didn't put the distributor back to where it should be you can experience what seems like total ignition system failure until the ecu backs off the advance. Take a look at the rotor arm and the cap terminals and see if there is signs of tracking or heavy erosion. If so then it is worth resetting the distributor (and possibly replacing the arm and cap if damage is particularly obvious).

A more interesting problem can arise where a non-stock ECU in conjunction with a stock distributor can provide a wider range of advance than the rotor arm was designed for. In a digital system like this the width of the contact on the rotor arm is in direct proportion to the potential advance since it must be covering the cap terminals throughout the range. You don't tend to see such problems on the older points/condenser systems as you would replace the entire distributor and as a result fit the correct parts.

On the original topic - my gut feeling would be that the accelerator pump is not enriching the mixture correctly at low revs, most likely over supplying fuel leading to a number of problems. If you can drive through the problem by more controlled application of throttle until the revs have raised then this would almost certainly be the case. It could be as simple as incorrect float settings (not that this is especially simple to fix).

That both cars accelerate well above a certain rev range under full throttle would lead me to discount the exhaust idea but it is still a valid issue in terms of getting the very best out of the engine.

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Post by F138 » July 3rd, 2006, 11:22 am

Additional information (sorry for abusing the thread!):

I changed only the carbs at a stock engine, I did not touch anything more. As we both have the same behavoiur of our engines I will search the problem at the carbs.

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Post by Guy Croft » July 3rd, 2006, 4:10 pm

I have seen this happen with an old original exhaust on the 130TC, ie: no apparent gain in changing from 40s to 45s, hesitation, then put on a stright thru silencer system and keep original header - everything is fine. I have in the past virtually stripped a whole engine - when I was less experienced with back pressure problems, only to finally pin it on high back pressure from old mufflers.

With back pressure, just to emphasise:

'if it can't get out (exhaust) - it can't get in (inlet charge)..'

Check carbs and ignition but don't forget what I have said about the ex. Don't go pulling the 45s off too quickly, if the engine is good it should have loads more torque throughout the range.


GC

dafnos

carbs

Post by dafnos » July 3rd, 2006, 4:24 pm

finaly!! i'm speaking to the worlds most famous Fiat tuner! :D hi guy thnks for reply.and hi to the rest of us :D guy i don't have any imformations for the cams (duration) but i know that they have an equal lift at tdc 4.5 mm and i made a mod by my own and now it's 5mm,i remove the pulley wedge and i turn the cams so i got an equal lift of 5mm.the valve opens at full lift 11mm.(the pistons,carbs and cams was for a race prepared 124bc). now about the carbs:im thinking to change the accel. jets or to fit a non bleed back valve for accel.jets,you thing that may help? the othher problem is that i can't find what i need in jets air correctors etc.i'm from cyprus and there isn't a dealer or someone who can provide this things!!! :( the only spares that i have are from some old carbs that i found on standard engines. feel free for suggestions or ideas!!!!!!!!!

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Post by Guy Croft » July 3rd, 2006, 6:05 pm

hello Dafnos

thanks for the interesting reply.

You might have a bit of a problem on your hands there, those cams sound like either my sprint-race 3D or Alquati StIII. there is an outside chance that theya re Columbo, they have a profile a bit like that, I might be able to tell from a good quality closeup photo of the shaft/lobe region, 300KB max please.

So, if they are what I think:
1. They need 38mm chokes in 45s.
2. They are super sensitive to back pressure and really need a 36" 4-1 header with single big bore race muffler.

We might need to rethink the jets, but I can help there. Do not on any account 'play' with the pump jet bypass (bleed back valve) in the float chamber or increase the pump jet, my money is on back pressure from your silencers (muffler). I guess you have an original 130TC system and it's not going to fly, sorry. If you make the mistake of going richer on any jets you will knock the piston rings to pieces (from bore washing) in minutes.

As far as jetting goes you need to get me the cam ID nos off the rear end of the cams. Moreover if they are such high lift I hope you are not running OE valve springs because they will not tolerate the lift or acceleration. I'd be very concerned for piston - valve clearances, I hope you have read the article in the GC V/W! 'Dry build and cam timing, or something like that. If not - why not?!

Carbs - Northampton Motorsport - see links. Export to Cyprus if that is what you need, they do it every day. If spares exist for your carbs, they are the best people in my book, go elsewhere at your peril. Tel 0044 (0)1604 766624. Troy and Steve are very, very good to GC and GC clients, always. I cannot say that of many firms.
Make the forum work and phone them up. There is no bonus for me, it's just that this website is all about 'who helps who'.

GC

dafnos

you are very very help full!!

Post by dafnos » July 3rd, 2006, 7:05 pm

guy now i'm in bristol and i don't know when i'll go home however there is a number in the rear end of the ex. cam that i remember: 494 i dont know what it means but i hope it helps(i thing my ex engineerer mension something about combo&bariani.and i'll try to take a picture from the cam if the number it's not helping).and yes i'm running on oe valve springs.the system is or. 4-2-1 and 62mm pipe but stdrd mufflers! we have very very big problems with police! they jailed my ufo65(reg.num) for one night and i took it back after i call a recovery to transfer it :x . so i'm not going to anything with carbs! thnks a lot for the information and keep up the good jop!!!! we need some experts opinion.. advises with the muffler,pipe and the 4-2-1 system(in english?)valve springs or anything you thing it may help!!
and something else:front brake upgrade! i need biger brakes if anyone knows a model that i can "borrow" the front system tell me! i change the rear drums with Lancia's gt 1600 rear disks

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Post by Guy Croft » July 4th, 2006, 7:26 am

Dafnos, hi

If it's 494 is Alquati: long circuit full race, 12.25 nominal lift, 40/80 80/40, running clearance 0.40mm. This is a mismatch. I would anticipate some severe running problems with the engine. I won't say too much because this is an advice section not a sales pitch!
Me, I'd be for pulling the motor and starting again.

There is a good post on this forum about brake conversions for the 130TC if you search.


GC

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Post by leifa » September 28th, 2006, 1:52 pm

I've got a similar problem as the one described at the start of this discussion. My set up is as follows: Ritmo/Strada 130 TC engine in a 131. Has Kent FT11 camshafts and IRESA 4-1 header. Carburators Solex C 40 ADDHE 27 which are the ones delivered when the engine was new. The carbs are like this: Venturi 32 mm, Aux Venturi type 4,8, Main jet up from stock 145 to 150, Air bleed jet down from stock 190 to 170, Emulsion tube A04. Fuel pump is Facet red top and stock Ritmo pressure regulator. Ingniton is stock Digiplex from Ritmo 130TC.

Below 3500-4000 rpm I have to be very careful applying throttle, otherwise the engine stalls. I suppose the problem is related to the set up of the carburators and wonder if there are any obvious mistakes in this setup?
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Post by Guy Croft » September 28th, 2006, 3:07 pm

Leifa, hi

OK- 4-1 header, sure, but what is your muffler/silencer setup?

GC

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Post by leifa » September 29th, 2006, 7:15 am

Guy Croft wrote:Leifa, hi

OK- 4-1 header, sure, but what is your muffler/silencer setup?

GC
The header ends in a 2 inch tube which immidiately is connected to a 2.5 inch tube and one silencer at the rear of the car. The sound level is close to the limit of what is accepted at "track days" and at "challence rallyes" (rallyes like the "Monte Carlo Historique") here in Norway.
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Post by Guy Croft » September 29th, 2006, 8:16 am

Thanks Leifa

OK, we can rule out high back pressure then I guess, to be honest, I can't immediately think of anything (in addition to other material written by me in this thread) except the pump jets not working properly - ie: goes way lean when you open the throttle.
Faulty Digiplex maybe, but I have seen the same symptom on such an engine before and determined that the ignition unit was not in fact faulty. Leads, plugs, coil, maybe but not the electronics.

GC

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Post by leifa » September 29th, 2006, 8:40 am

Guy Croft wrote:Thanks Leifa

OK, we can rule out high back pressure then I guess, to be honest, I can't immediately think of anything (in addition to other material written by me in this thread) except the pump jets not working properly - ie: goes way lean when you open the throttle.
Faulty Digiplex maybe, but I have seen the same symptom on such an engine before and determined that the ignition unit was not in fact faulty. Leads, plugs, coil, maybe but not the electronics.

GC
Thank you, I've done a visual check and seen that there is a squirt of fuel in all four openings when I operate the trottle. I guess it's time to make some measurements. I've changed the leads, but not the rest of the ignition parts. What kind of plugs do you recommend? Do the setup of the carburators look reasonable?
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