Pics and vid to come
Hi everyone, hoping someone can help with my troubles. Have read a lot of previous posts on similar issues and been troubleshooting with no luck. Thanks for all the advice so far, and any future comments.

So heres what I've got:
12a na bridgeport
Nikki carb. emissions etc removed, running pre mix.
Please don't shoot me, it's in a van. Picked it up cheap but it has a few issues atm. Any help is much apreciated, i cant get my sev until its running right.

The problem(s)
Rough idle:
it's wicked, and i cant figure it out. Its starts easy and Its idling steady at 1500rpm but it doesn't constantly pulse like it should, sounds like its missing or bogging down. The pulse breaks up.

The engine is a little shaky when its not pulsing steadily.

When i rev it slowly it misses / sounds like its breaking up.

When driving at a steady pace it feels like its surging faster and slower.

When i give its some gas and get the revs up it miss fires / backfires.

If i give the accelerator a quick stab it seems fine.

Things i have done:
Checked for vac leaks
Checked timing
Replaced fuel filter
Drained tank
New plugs
Squirted a can of carb cleaner down it
Checked gas is squirting in
Checked float level

Things on my to do list:
Check break booster
Compression test
Replace leeds, even though they appear ok.

All of the above seem fine, i will post a vid to get a better idea of what i'm on about.

Its got me stumped so any comments or suggestions are much appreciated.

 

here's the pics / vids
its still cold so not as noticeable, but i hope it gives a good idea of whats going on.
it's also a lot worse than the video portrays.

[IMG] [/IMG]




thanks again!

 

vid 2 shows the bad idle the best, if you get my meaning. vid one was cold start and 3 is when its a bit warmer, but it is completely erratic and unpredictable

 

Sounds like you need to tune the carb and fuel flow on it.

 

What vehicle is that engine in?! Looks like some sort of minivan?

 

It's probably a Bongo van. We didn't get them here.

By the way, it runs like how a bridgeport is expected to run/idle. You will need to learn to put up with it. If you want smooth, go with a mild port. Is this your first one?

 

the brap brap is caused by exhaust dilution from the port overlap, and when it goes from brap brap to the non rhythmic thing its because the amount of exhaust gas getting into each intake stoke isn't constant.

its kind of the nature of the thing, its like having a 320 degree cam in a piston engine. there are a few things you might try to make it better/more consistent.

lower the idle speed, it depends on the size of the bridge, but my P port would happily idle at 700rpms if the carb could meter fuel there, it can't so idle is more like 900-1000. 1500 is high...

play with timing, the Pport idled better when the idle timing was closer to stock, its not much better, but it is better. i have a locked distributor, so the engine is really telling me that it wants a timing curve.

reduce intake vacuum. with a big port, like you have the intake and exhaust are open at the same time for a long time together. there is vacuum in the intake, and pressure in the exhaust, so the intake sucks up exhaust gasses, and causes the brap brap idle. if you reduce the intake vacuum, you reduce the amount of gasses that get sucked up. i drilled a small hole in the throttle plate, how big of a hole is part of the tuning process, as you do trade a little response for better part throttle running. and you also have a different carb, i'd start in the .010" area.

i can actually get the p port to idle normally like a stock port engine, which of course defeats the point, the brap brap is cool.

http://foxed.ca/rx7manual/manuals/Rx...%20(70-73).pdf

 

Yea 86 bongo.bthank 4 replying
I know bp goes brap brap lol its when it stops going brap and going brrrrr brrrr ap thats the prob haha. That and its missing under load and missfiring up high. A month ago it had a good steady faultless pulse. Since then idiots have driven it and may have changed something. I did notice a new alternator pulley but it was running mint before, now not so much

 

Nope not first one, and definitely not running right. It used to pulse ( brap ) regularly in faultless rhythm, it was mint. now it has splutters in between, misses during accel and backfires at high end revs. So na not how its expected to run at all. It sux now, i dnt even wana drive it

 

Thank for the reply, im not trying to smoothen it out or stop the brap brap sound just the faults like when its not going brap brap. It was running perfectly a month ago, based on that would you have any ideas what could have changed?

 

start with the basics, spark plugs, idle mixture, etc

 

Thanks man. i tried the basics if it was easy i wouldn't have posted. adjusted mixture several times in accordance with a great post on here. Ive been trying to avoid stripping the carby as im not too confident with them, Got plenty of squirt and Float levels seem fine so could it possibly be a blocked jet?

 

Thanks man, ive tuned carb the best i can in accordance to a great post on here, and there seems to be good fuel pressure. could this be a symptom of a blocked jet?

 

how's the muffler? these engines are hard on them... if the car/van didn't sit, i'd think the carb was ok, most of the time a carb problem is something else...

you could also try a compression test.

 

I never would have thought about checking the muffler. It did sit for about a month also but doubt thats long enough, has previously been run without an air filter also. Maybe i should comp test it, i hand cranked it when i changed the plugs though and it seemed ok

 

Compression tested good, rotor 1 96 over all and rotor 2 98 so pleased with that. Must be something simple iv missed somewhere or something a miss with timing. will also look at the exhaust on a bit more closely, gave the muffler a shake and sounds like somethings rattling around inside. Thanks for the input evryone

 

I didnt know you could run a bp with the stock carb mine has a holly 600 all mechanicle so I don't have much to worry about but good luck with it bro

 

Yea cheers man, its not completely stock, the jets have been modified for more flow etc. its quite common where i live as it's cheap to do. you either have a nikki or a 48 ida. I believe someone has actually got 13 sec out of a nikki here.

 

That's sweet man rotaries in general are very uncommon here I'm kinda off doin my own thing people give me weird looks b/c my car goes brap brap brap lol

 

Im thinking the Nikki is too small as well. Unless its been hogged out. Sterling, Yaw.

 

Yea its beed modified to suit and was all running mint previously. unless theres a blocked i'm almost certain it's not the carby now. Im changing the distributor cap and rotor this week and going to pull the exhaust off and see if theres a restriction there that could be causing it. If not i'll try a new fuel pump, if that fails then ill have to bite a bullet and take it to a rotary shop to get the timing checked by a pro and the carb tuned. It runs ok now though, only missfires if i accell too fast in the mid rev range but not evry time. the surge has gone now atleast so that could have been a leak i fixed. I just want my pulse back damit!

 

What kind of nikki is that?

 

Just the 4 barrel 12a's came with, stripped, blocked off, jets bowls etc changed

 

I just also read somewhere that rich mix can flatten the idle out so will try turning the idle up to 2000 rpm and playing with the mixture again in the next few days and let ya know how i get on.

 

that exhausts looks like a happy dog wagging it's tail.