fiat spider high preformance issues

[DRHSMITH]

hi i have posted here before i got sick of issues and rebuilt engine to be sure. i have weber dcoe 45's high comp pistons balanced crank , computronix ignition kit, high preformance headers, cams basically the whole works . i have about 6000 k on new engine or so and still have issues. i have a custom double exhuast side pipes actually which i have installed real time digital fuel air mix guages too see what car does each side . when cold the car has some decent power but when warm has nothing to the point where im sure stock spider would preform better at higher rpm. i have afuel pressure guage and am running around 1.5 psi anything over this and car runs way too rich.
the carbs are your basic weber dcoe 45 set up f11 imusification tubes lowest main jet u can run 1.50 , idle jets are the basic they come wiht i forget what they are off the top of my head but the recommended set up ones for this carb i believe but no matter what run over half pedal car goes too rich and wont make hp . when first on pedal car goes too lean then as you progress in i get around 14.2 to 14.7 which is optimal the more you go over half pedal the guage progressivly goes richer too the point where it can bury rich. ive timed engine alot in my time with the car i get all the timing marks as close as possible crank at tdc and very very close but not exact on the intake and exhaust cam timed the comutronix with ign timing light between 10 and 12 degrees . i was told by my machinist and i who built the engine that would take until bout 10 000 k until the engine would make decent hp so i run watching the fuel air mix and keeping it in the best optimal range .i drive car about 400 k a week but this car before i had issues with the engine prior too last rebuild had a really nice amount of power we redid engine properly taking close care too the manual tolerances ect. Should the car be so weak before break in time is done i wouldnt think it should be this ridiculoiusly slow . car runs to cruise quite alright but legit stock spider would probably beat it which is ridiculous consdering what is into the vehicle now . i realise my carbs are not quite right set up wise ive tried running though the tech stuff with them , linkage is a bit of an issue ebcasue going down too idle is different sometimes then others

point form to try and make basic
1 car has about double the power cold then warm
2 you sometimes do get what might be a light detonation sound ( very slight ) after car warms up a bit when u go deeper into the pedal
3 weber carbs lean out when first on pedal then about 1 quarter down starts to go near optimal fuel air mix then after half pedal produces less and less power and goes progressivly too rich
4 is weather is over 30 degrees regardless you have no power at all, if below 15 power during warm up but then back to slow when warmed up

[DRHSMITH]

legit any help would be appreciated i am in central ontario canada i would pay for someone too set up my carbs properly but cannot find anyone who will even look at them i have colour tuner , the stack air tool i tried following tech guide lines best i could but cannot get them correct once again thanks too all who read just getting frustrated as i have not had the hp the car used to produdce in about 5 years car needed other wokr which ive done i just want too get some help thanks

[baltobernie]

Every performance build has its challenges, and the further you depart from stock, the trickier it gets. And the Weber-carbed Fiat TC has so many possible permutations, one could spend huge amounts of time and money getting it sorted. Hopefully, Manoa Matt will jump in here to get you some expert help, but until then ...

First ensure that all of the mechanicals are on spec. Cam timing, valve adjustments, distributor advance, carb linkage, etc. For example, no amount of jetting will fix a carb problem caused by linkage that holds open, however minutely, the main circuit. This particular item is on my Wall of Shame, with a dozen FedEx envelopes formerly containing jets and tubes.

You are probably aware that the DCOE is a synchronous design, best suited for racing. It's gonna be a bear to tune for the street, and you've got two 45's competing for a limited amount of vacuum.

Another thing that jumped out at me were your mixture ratios. Check with Matt, but I think you need to be in the 13s. 14.5 is "ideal", but you can't cut it that close with carburetors.

[DRHSMITH]

the closer i get too 12 the worse the car runs more pedal equals lesser or no more power it seems the 14.7 optimum has the best operation,anytime i see mix going near 12 im getting less power then at 14, is there a special linkage kit u can get too make sure its proper. ive def ensured valve shim heights engine timing, timed computronix with timing light ect is the best possible from full shop manual. i had head off 2 weeks ago because for some reason a back head bolt snapped at which point i pulled head off fixed the issue inspected everything and put back together. the head and vavlve and cyl head were all light golden brown showed no signs of carbon build up and seemed in excellent shape component wise . the car before with these carbs would fly i ran engine for 3 years after first rebuild wiht a linkage that would only pull about one third the throttle distance at the carbs . made it so the linkage would pull full and the car was very fast until about 5 months of running at which point started slowly dying. i think the guy who built the engine used wrong size piston rings because when i pulled it apart some rings were in three pieces cylinders compression ranged form 185 down too 112 and the other two in between

[So Cal Mark]

the one item that jumped out at me is your comment about custom double exhaust pipes. Have you really split the exhaust into 2 cylinders per pipe? Post a pic please of your header and exhaust system

[DRHSMITH]

yes lol i have about 9 years ago the difference was instant after installing them way more power even on the big single carb. ill post a pic later today. i ported and polished the head on the intake side removing the flow angles as much as possible and increasing the port size quite a bit too an oval shape. the intake manifold as well slowly following the flow gets larger too meet the intake of the head i did this years ago on the single carb and had a very noticable increase in power driving that way for about 3 or 4 years until i had the engine redone. exhasut has a ton of pressure even at idle will move a carboard box almost three feet away when running . a head bolt snapped randomly about 1700 k ago i have no clue why i took head off 2 weeks ago fixed bolt issue inspected the head and components everything seemed great the colouring of the vavle heads piston tops and cyl head where combustion occurs was all a light golden brown equally too all cylinders didnt show any signs of issues that stood out . is it normal for engine too need about 10 000 k to break in for getting power/ ive drivin the car light for the most part keeping in my optimal range for fuel air dictated by where i am on the throttle trying to run it too get break in period but def has to be something not quite right . as i said this same set up before was very fast for the car but i rly think the guy who buiilt engine had incorrectly sized piston rings or i had another issue cylinders after a while compression wise cyl 4 was art 185 cyl 1 was 112 and the other in between . i pulled apart engine to find rings were in 2 too 3 pieces still riding in piston slots except for cyl 4 . so re did engine with my friend who is a very very good machinst who has built many proffesional race engines . he told me run it normally not pushing engine muhc until about 10 000 k which is what i have been doing experimenting sometimes going down on the throttle only the very odd time too see the result

[So Cal Mark]

only chrome rings would take that long to seal

[v6spider]

only chrome rings would take that long to seal

Totally a waste ...there is absolutely no reason to run chrome rings on a street machine.. Absolutely no benefit there. I'd rering it with cast rings it'll seal quick with no issues.. IMO I'm running cast rings and hypereutectic pistons.

Cheers!
Rob

[vandor]

Why do you say the lowest main jet you can run is a 150? If it's too rich over 3-4000 rpm, then likely the main jets are too big. AFR should be 13 at wide throttle settings, any richer than that means it's way too rich.
I'm not an authority on DCOEs, but the guys that know a lot about them would need to know your exact jetting to be able to help.

[sptcoupe]

This really sounds like mostly a jetting and balancing/synch issue.

What size venturis (chokes) are you running? The vacuum signal in the venture is what determines how much fuel you need to mix with the air being drawn by your engine at different engine speeds. A 2mm difference in choke size can change your jet selection by two full steps in different rpm ranges, depending on what else you have done to your engine/intake/exhaust. So let us know that, first.

What size aux venturi is installed. The aux venturi size affects the way your venturi performs, which is also essential to initially determine the main jet size.

Your idle jet size is critical, as it meters the gas from idle to about 4000 rpms, and effects the transition from the idle circuit to the main/air corrector circuit. What size idle jet you need is determined initially by the venturi diameter. What size are they? A one step error in idle jet size will cause you many of the symptoms you describe.

What emulsion tube tubes are installed? Another major tuning component.

Have you balanced the bores on each carb? This is done using the air by-pass screw and a Synchrometer or Unisyn. If not you will be wasting a lot of time chasing a lot of symptoms for problems that don't exist.

Have you synched the carbs to ensure they are opening at the same rate and the same amount? Use the carb linkage with a Synchrometer to do this.

Just from what I read, it sounds like you are running big jets and are just simply too rich, and have some set up issues as well.

[DRHSMITH]

i have f11 tubes, lowest main jet you can get 125. i called weber carbs and u cant get any lower mains id have to make them my idle jets are also lowest u can run. the set up i have is typical for this carb set up for this engine as i bought them through a guy who only works on fiat spiders. both carbs show equal airflow at idle with the sych tool . my compression shows about 170 but the adaptor that threads in is half the depth of my actual spark hole and plugs so it would be higher then that. rechecked shims all perfect too manual ill pull apart all the jets on the carbs and post the numbers. timing is perfect for ignition computronix timed wtht the ign timing light and the engine cams and crank. this set up worked before on the previous rebuild and hd lots of power unitl the rings broke in the engine and a cam lobe had an issue i believe the guy sized the rings wrong i have about 5500 k or so on the car and still is very slow to go through the mix issue again when i barley touch the pedal goes ultra rich i go a bit more goes ultra lean then as i progress more( one quarter throttle too half or so) goes into good range around 14 or so but then anything after over 3 quarter pedal car goes slower and slower as it gets too rich and shows over 12 on air fuel digital mix guages i cant figure out how to post images for socalmark
i have the exhaust pics hes asked for

[sptcoupe]

I'm not sure what you mean that 125 is the smallest main you can get. I have them from 110 to 175. You can get most any jet from Pierce Manifold in Gilroy, CA. I know they carry all the jets I recommend you try, below.

I'm still not sure what you are running in terms of the carb set up. But the F11 tube is a hint. Given the new info, this is what I would go with to get it pretty close:

32mm (venturis) chokes
4.5mm auxiliary venturis
F11 emulsions
130 mains
180 air correctors
57 idles
175 needle valves
floats adjusted to 10mm at close and 32 at full open (add one millimeter if the carb top gasket is in place.

This should get you very close.

[seabeelt]

+1 on sptcoupe's advice. I would also look for air leaks at the base of the carbs and intake manifold as well. Had that happe on one of my IDFs and experienced loss of power. Too much air at times. My adjusting to compensate caused a rich condition until I found the real problem and then went back to my original settings.