[rogbot]

A few years ago I had the DCOE Webber carburetors on my Giulia Sprint GT re-jetted because the mixture was too lean at low revs (2000 – 3000) and the car was running very poorly in this range.

The new jets greatly improved things but the tuner warned me that the car was now running too rich at high revs.

I recently took the head off to put in a new gasket and it took me a fair while to clean the carbon deposits from the ports. I decided to take the car back to see if a compromise could be found that would make the mixture a bit leaner at high revs.

After looking at the car on his dyno the tuner decided that this was not possible and that there was something fundamentally wrong with the car. He suggested that the cams might not match the block or that there are too many mufflers (i.e. 1 in the middle and 2 at the rear).

I know a fair bit about the history of this car and I’m pretty sure the block is original. The number on the cams is: 10 502 032 000 1, perhaps someone on this forum knows if they are the original specification? Ditto for the mufflers?

Up until now I have tended to view this problem as a design limitation of the car which I can live with. I rarely rev the engine over 4000 rpm possibly because if feels a bit rough beyond this point and doesn’t seem to produce any additional power (the tuner says the power actually drops away). I’m also not sure how much of the carbon in the ports was produced by the larger jets.

If however something can be done to fix it I would be very pleased.

Any suggestions would be welcome.

 

[seani]

If you are happy with the main jets in the midrange then to weaken the top end you need slightly larger air correctors. As a general rule the main jets will affect the mixture from about 2000rpm upwards but the air correctors have more effect from 4000rpm.

Sean

 

[alfazagato]

Cams are OK as are three silencers. Have you checked the obvious, timing, cam timing, cylinder leakage????

 

[rogbot]

Thanks guys,

My tuner should know about the air correctors but I might look into it myself in case he has missed them.

Timing and cam timing are fine.

I've got 200 psi in each cylinder (hot with throttle open fully) which incidently is causing pinking in 5th but I think I can safely say there is no leakage.

 

[Alfajay]

....the tuner decided that this was not possible and that there was something fundamentally wrong with the car. He suggested that the cams might not match the block or that there are too many mufflers (i.e. 1 in the middle and 2 at the rear).

Hmm, that's an odd diagnosis.

The cams might be timed incorrectly. But "not matching the block" just doesn't make sense.

"Too many mufflers"??????? As alfazagato wrote, Alfas came with three mufflers (OK, one is a resonator) as original. Unless your's has four or more, I don't get this one. Might he have meant that your exhaust system could be blocked or too restrictive, impairing top-end performance?

 

[flivesay]

Hmm, that's an odd diagnosis.

The cams might be timed incorrectly. But "not matching the block" just doesn't make sense.

"Too many mufflers"??????? As alfazagato wrote, Alfas came with three mufflers (OK, one is a resonator) as original. Unless your's has four or more, I don't get this one. Might he have meant that your exhaust system could be blocked or too restrictive, impairing top-end performance?

you mean it sounds like BS from the tuner yeah

 

[alfazagato]

Another tuner?

 

[Chris1750]

Ditto - I'd be going elsewhere.

Hope you didn't pay him for the advice.

Chris

 

[pancho]

Maybe he is a de-tuner?

 

[rogbot]

The tuner is fairly well regarded by Alfa racing enthusiasts but I'm starting to think he is not all that good at tuning for general usage.

The more I think about this the more I am inclined to just stick with what I've got. The car drives well up to 4,000 rpm and I don't find that limit too restrictive. If I want to go racing which I don't, I'll put the leaner jets back in and accept the reduction in performance at low revs.

 

[pancho]

Does anyone have a factory dyno graph for the power the 1600 should be making? Power should be available past 4000rpm.

 

[60sRacer]

Gee. My Duetto - back when it has a 1600 engine - loved life at 7000+ rpm! Something is not right, and your tuner is pure BS about it. Any good Weber tuner knows there are jets, airs, emulsion tubes, etc that will affect the entire range of operations. Get one of the Weber books.

Robert

 

[roy]

Hi compression numbers , plenty of power up to 4000 rpm . Sounds like intake cam is too far advanced .

 

[rogbot]

The cams are in sync with the engine alignment marks and I'm getting a pretty good vacuum reading at the break booster tube. I'm attributing the lack of power at high revs to the overly rich fule mixture at the same revs and the high compression to too many head skims.

When I had the standard jets in the power built steadily to 7000 rpm and about 70 hp at the back wheels.

I think I might take the suggestion of purchasing a Webber manual and see if I can figure someting out for myself. In the meantime I'll stick with my present settings.

 

[alfazagato]

May I suggest you find someone with a proper diagnostic set-up so that you can see precisely what is happening with the mixture. But, here's how I found 10 bhp recently......I re-adjusted the linkages to give full butterfly opening.

 

[60sRacer]

What are your current jets?

Idle, Idle air
Main jet, Main air, Main emulsion tube

BTW - do you have the choke levers closed? That would give you a lot of enrichment.

Robert

 

[rogbot]

Thanks Stuart, I think I might try and investigate things myself for a while, my faith in people with the "proper diagnostic set-up" is a bit shakey at the moment, the last guy did at lease adjust the linkages for me.

Roger