85 Brat, EA81, Hitachi carb.

Both fuel filters replaced. New plugs, wires, air filter. PCV seems to be operable.

I can choke it and start the car fine, though sometimes it stalls a few seconds later. Starts right back up again. 

It's having a hard time with high RPM, and coming off idle. It wants to drop RPM down when I apply throttle at idle when cold(and will sometimes die), but when warmed up this is much improved, but not gone. It seems like it's running lean to me, but I can't figure out why. I did the carb rebuild on it recently, which made things better, but didn't completely fix it.

Vacuum leak. For real. Experienced the same symptoms with my '86 for years, switched over to a Weber carb and voila! No more issues.  Lots of the Hitachi's vacuum lines not necessary with the Weber so they're plugged off. 

I can find no vacuum leaks. I used my vacuum pump to test every line and diaphragm I could, all tested good. 

One pump of the throttle before start up, and on cold start it fired up right away and idled fine just now. Still feels a bit hesitant as I throttle it up, but better than before.

Just took it for a drive(it's not yet registered, and needs to pass emissions to get registered).

Stumbling on partial throttle. It will idle fine, and run ok at full throttle fine. It's everything in between. So it seems to be getting enough fuel. 

 

Maybe something like the intake manifold gasket leaking? Carb gasket? 

Check for an exhaust leak where the header pipe/manifold connects to the head. Had a similar issue with Ruby when I first got her, wasn't to bad at first but progressively got worse. Got around to fixing the exhaust leak and has been fine ever since.

 

Cheers,

 

Al

Valve clearances too tight causing the valves not to fully seal properly?

How much shaft play in your carb’s throttle shaft? This can be an issue too. 

Cheers 

Bennie

14 hours ago, Speedwagon said:

I can find no vacuum leaks.

Go around it with a can of carb cleaner while running. It might not be one of the hoses. 

As mentioned by freddo, throttle shaft wear might be a thing. You'll find it with the carb cleaner. 

Good luck!

Dan

The Emulsion tubes are clogged.

Pull the cap off the carb.

 Unscrew the 4 brass emulsion tubes and blow them out with carb cleaner and compressed air.

Might also be good to pull the bowl drains, and access the jets through the holes, and clear those out too although they never really clog the way the emulsion tubes do.

 

31 minutes ago, FerGloyale said:

The Emulsion tubes are clogged.

Pull the cap off the carb.

 Unscrew the 4 brass emulsion tubes and blow them out with carb cleaner and compressed air.

Might also be good to pull the bowl drains, and access the jets through the holes, and clear those out too although they never really clog the way the emulsion tubes do.

 

+1

Sounds like the primary barrel only.

Make sure the fuel level is in the middle of the sight glass and the accl. pump squirts strong too.

The air bleed system/hoses matter too.There is a calibrated orfice in the line.

Idle would be bad w/a vacuum leak.You would be lucky to find one w/a vacuum pump,

Doesn`t the automatic choke work?

Yes, the choke works. I can watch it slowly opening as the engine warms up.

 

I'll check the others things you guys recommended, thanks.

 

edit: I do know there is an exhaust leak up front. Had to fix the muffler first, but now I know there is one. Which gasket belongs between the head and the pipe? Just the O one, or the oval one with bolt holes?

Edited April 3, 20196 yr by Speedwagon

My Hitachi used to bog down when I'd give it gas to go from a stop sign or light. It would go "flat" - like blank spot in getting any fuel, and then take off normally. Drove me nuts. No issues at all after changing to the Weber.

I don't know if the Weber would pass the Colorado visual emissions inspection though, so I'm not sure if that's a plausible alternative just yet. Without the vehicle being registered yet, it makes it more difficult.