su fine tuning

[madkaw]

I decided to bring my problem to this forum since thru deduction process I believe the carbs are my final issue. I guess the first question would be; what adjustment or problem with my su's would cause the engine to not want to rev up freely and be flat on power.

Originally the engine idled smoothly and reved up sitting in the garage but out on the road it was flat over 3000rpm. I have gotten past the 3000 rpm ceiling but it goes slowly and without snap or power. It would tend to make me believe I am running out of gas. I believe the floats are adjusted properly and after cleaning carbs thoroughly I preset them according to 'just Su video'. Would a bad idle adjustment effect me at higher rpms?? Presently the rear 3 cylinders are fouling plugs. I guess that could be an obvious idle mixture problem-both carbs are set at 2.5 turns. Again, would this fouling problem could equate to higher rpm weakness??

History: the car has 88k original-71 with 4 screw carbs. The carbs were thoroughly cleaned but no parts were replaced-original needle and seats,ect.... Great compression, timing set and verified, ignition all new, fuel tank cleaned, filter changed, fuel pump changed(fuel pressure not checked).valves adjusted. Do not beleive I have any vacuum leaks.

I am going to try one last attempt at idle mixture adjustments after reading all the articles my tiny brain:stupid: can absord. After that i am going to mount a newer set of SU's to see what difference it makes. Right now it is about 10degrees around here so maybe it won't be today.

I guess it comes down to being a 37 year old car that has been wanting some attention for a long time, now it's getting it!

[justinr54321]

On these old cars, its not uncommon to have one carb adjusted slightly leaner to get it balanced with the other. Also, do you have a carb sync tool to get the airflow right? And a color tuner would help too.

[madkaw]

Yes I do have a sync tool and I probably need to be a bit more liberal with the idle mixtures!

[madkaw]

Well I was getting ready to give up on these carbs and put on another set to see if that would eliminate my problem,but I decided to look over things one more time. After removing the air bonnet backing plate and ran the choke up and down and made sure everthing was returning properly and the throttle was actually opening up all the way when i noticed the front carb fuel hose that runs from the float bowl was kinked. I am thinking that it could be this easy. The front carb is getting no fuel so the rear is trying to pick up the slack and loading up with fuel while the front is doing nothing. I changed out the new Z therapy hose with an old one and it was like magic, the car ran perfect. I got all the rpm range and all the power now.

The ordered these hoses from Bruce and I questioned the length of the hoses when I first installed them. After talking to Bruce i cut the hoses to match the originals. At the time the hose seemed fine but I guess it slowly collapsed over time and that's what made it hard to diagnose. The rear carb hose is still okay, just the front kinked. Maybe bruce will read this and chime in. Bruce has always been super to work with so don't think I am bashing Z therapy.

It's been a good day!!

[Zs-ondabrain]

I just had the same issue but it turn out to be my MSD 6A ignition. It would rev to 3000 just fine but would'nt go a bit past it, without chugging and back firing like I was choking the hell out of it.

So I bypassed the MSD and now I'm down to the Mallory Unilite and promaster coil with the stock ballast resistor. I think it might have had something to do with the buckets of rain I drove trhu the other day. Thank god for my new Honda wiper motor set-up.

Just another thought.

Dave.