Strider

If I spray carb cleaner around the rear of the carb body when its idling, that is the definate location of the leak, as the rpms immediatly pick up and the motor smooths out. But all I can see back there is throttle linkage and the throttle opener for the A/C and the choke diaphams. It looks like there is a plug on the float bowl that gives access to the main jets, and that plug is all crudded up black, like its especially dirty, but wouldnt' that leak fuel out, not vacuum air in?

Could it be that the bushing on the throttle shaft is worn? The shaft, linkage and springs are all really cruddy. Has anyone ever rebushed a Nikki carb?

I'm in the process of slowly taking the carb off and apart. I'm taking a dig pic every step so I can be sure of putting it back together right. I always knew that a digital camera had to have some practical use (I'm into 35 mm slide photography and generally hate the quality of digital pics.) I must say that this is possibly the most complex carb I've ever worked on, and I've torn into more than a few. Fuel Injection is simple in comparison.

Thanks

SilverRocket

There is a large vacuum hose that goes from the back of the carb to the back of the intake manifold. I'm betting this is your problem; it very commonly leaks. Pull that hose off and your car won't even start, and even a small leak will cause a very rough and low idle.

And yeah, the Nikki is clunky as hell... an aftermarket carb is the only way to go IMO.

Strider

So I finally got the carby off....whew! what a PITA! It still isn't aparent where the vacuum leak might be. What is that buterfly valve on the single rear primary intake port for? Is it the "coasting valve"? and what's it for? Right now I'm either suspecting that or maybe the Port Air Switching Valve....hmmmm. The base gaskets came up really easy and were bone dry, so they might have been seeping also. Right now I'm prepping my workspace before I start dismantling the carby. Ziplocks and a black sharpie to keep the parts straight, and a fresh can of carb dip....(In the past I've been known to boil my carbies out in hot water on the stove, but I don't think my spouse will appreciate that!)

Strider

RotorMotorDriver

iTrader: (1)

Yeah, thats the coasting valve, aka, shutter valve. Its supposed to cut the air/fuel off to the rear rotor on deceleration to cut down on backfiring...or some ****.

~T.J.

Strider

OK, very late update here, but I don't hardly drive the car, I mostly ride my motorcycle, so I haven't felt compelled to work on it.

I finished rebuilding the carb a couple of weeks ago. I took off the shutter/ coasting valve diaphragm in the process too, and checked it out. It seemed OK, with no leaks and worked freely, so I shrugged and just put it back on.

While I had the carb off I decided to go ahead and replace all those vacuum hoses on the rats nest because some of them were pretty hard and cracked. In the process, sure as ****, I found a large one that was split wide open down in the vicinity of the intake manifold and exhaust manifold. It went from there to a valve on the rear lower passenger side below the carby. Not sure what its called.

So after some initial setbacks, like the float valves not seating and flooding the carbs, I got it all together and it started right up. (boy, MMO down the carb throat makes an IMPRESSIVE amount of smoke. I haven't seen a smoke screen like that since I was in the Army ) Anyway, I got it to run, and somewhat tuned. It was a 90% improvement from where it was.

HOWEVER, after driving the car once to work, I noticed that it became REALLY hard to start when cold in the morning, and it had this intermittent missing through all RPM except not so noticible when the secondaries were open. I parked it and havent driven it until yesterday.

I should have suspected the coasting valve. I couldn't set the idle lower than 700 rpm when playing with the idle adjusting screw. Every other car I've ever worked on you could adjust the idle screw out until the car died.

So tonight I took off the top of the air cleaner and put my finger over the hole to the coasting valve....sure as **** there was suction....and the RPM immediatly dropped. HELLO! Here was a path of air that completely circumvented the carb, straight from the air cleaner to under the bottom of the carb into the intake manifold.

So I plugged that bastard...jammed a bolt with a round head into the hose, and a rubber plug into the air cleaner hole just to make sure.

No more missing through all RPM! I was actually able to tune it to exactly like the manual describes....find the highest rpm with the mixture screw (about 3 3/4 turns out), turn it in until rpm drops by 70, then adjust the idle to 750. MAGIC! Oh-yeah, forgot to mention that before all this I advanced the timing to about 2.5 to 3 degrees BTDC with my magically calibrated eye. (In other words, above zero and under five.)

So anyone who reads this thread, if your car is missing at all, the first thing I'd suggest you check it that coasting valve.

Strider

peejay

The anti-afterburn hose strikes again!