I am about to work on a 81 and I can't seem to figure out what its problem is... The car will start... rev up and drive fine up until about 3500...then the car begins to just loose power and does not want to pull anymore-

I just wanted some opinions before I go start tearing into it...

Just to clearify- the car will rev just fine....its when you go to drive it the problem comes in... Compression is good-

Carb???

Thanks guys!

 

Fuel starving?

 

The guy said he checked fuel pressure... everythings seems ok....


This is one of these weekend guys...had the car since college...knows a little bit about it ... but when it comes to the big stuff...he takes somewhere-

 

As others have said, check your fuel delivery - flow! not just pressure.. The filter may be due for replacement.

 

my car falls on its face at 1500 rpms

 

One thing to check.

I had a problem where when the vacuum/mechanical advanced in the distributor, It would short out the leading sensor, thus causing the engine to lose leading spark at above 1500 rpm.

RXDad

 

double that, change your fuel filter.

 

If you have a fuel pressure gauge, put it on there and make sure pressure doesn't drop when it stops pulling. If the air pump has been disconnected or the line to the catalytic converter is broken then the cat can be completely plugged and not let enough exhaust through to run above 3k under load. Or it could be a problem with the secondaries on the carb or plugged jets or passages in the carb.

 

check to see if your secondaries are opening

 

ok yea just dies at 1300 to 1800 i have to tap the gas to get it past is then its fine

 

+1

 

I'll second the clogged jets theory due to personal experience...

 

My money would be on secondaries not opening.

 

I'm with cdrad51 on my 1st choice. Then 2nd fuel volume not pressure. Then blocked exhaust.

 

same thing happen to me when it hit 3500 people told me to change the filter. i changed it and hasnt fell on its face since. so change it!

 

If your secondaries weren't opening the RPMs would continue to climb smoothly but without any torque. In that case the common problem is after a rebuild ppl forget to rest the pin of the spring piece connected to secondary throttle at the rear of the carburator on the ledge above it. For that mouthful there's a picture somewhere on the forum that does a much better job of describing it.

If it's bogging after 3500, the secondary jets are clogged. If that's the case, the first thing you should do is change the fuel filter to eliminate the cause of the contaminants. If it works after that you're lucky, otherwise you'll have to get into the carb. You can clean the jets without having to rebuild the entire carburator - I was forced to do this on a recent trip to upstate NY. With carb cleaner spray in hand remove the hat of the carburator (the layer with the choke). There's about 7 or so screws holding it on and the large 14mm bolt going down the center that also bolts the air cleaner. Be careful when removing it because of the gasktet; if you tear it then you might as well get a rebuild kit and do the whole thing - for that matter, you should have rebuild kit on hand just in case. One by one, remove the needles (brass, flat headed screw thingys) and spray hard into their holes. Be careful not to lose the check valve ***** when doing this. Give the needles themselves a good cleaning and blow through them to make sure there are no obstructions. Since you got it open, you might as well do them all. Clean any crud out of the float bowls. Spray the ever living **** out of them and wipe up all deposits. Put it back together and you're done.

 

Check out the thread on how to remove jets without tearing down the carb:

https://www.rx7club.com//showthread.php?t=598078

Very simple, but a little cramped to get the rear ones out. Chances are you'll find that at least some of them have some hard crud built up on them. I spent about 6 months diagnosing this same issue before I found the culprit.

One way to really narrow it down and make sure its jets rather than a fuel delivery issue further upstream: Get up to a decent speed on the road until its really bogging, let off on the throttle for a few seconds (to make sure that the float bowls have a chance to fill back up again) then floor it. If it still acts the same way, then the issue is in the carb (or maybe ignition).

If it was a weak pump or something of that nature, the float bowls would fill up because you gave the pump time to catch up, and you would have good power for a few more seconds after that. Good luck...