1991 750 project, wont idle

[Motorcyclelocksmith]

I purchased a beautiful 91 750 zephyr as a winter project only to be defeated. It had been wrecked but still looked decent. Runs with fuel sprayed through air box. Tested as follows:
-Compression within tolerances
-Elctrical system functional(coils tested,spark tested, plug wires replaced, and plugs)
-petcock functional
-vacuum lines replaced
-carb bowls and jets cleaned
All filters are clean and I am stumped. Any ideas?

[Freddy]

Make a mistake and can't delete, see next post

[Freddy]

I purchased a beautiful 91 750 zephyr as a winter project only to be defeated. It had been wrecked but still looked decent. Runs with fuel sprayed through air box. Tested as follows:
-Compression within tolerances
-Elctrical system functional(coils tested,spark tested, plug wires replaced, and plugs)
-petcock functional
-vacuum lines replaced
-carb bowls and jets cleaned
All filters are clean and I am stumped. Any ideas?

How did you clean the pilot jets? Well all the jets for that matter.

Also what did you set the pilot screw too? And if you took them (which you should have to properly clean the idle circuits) did you make sure not to loose the tiny washer and o rings that sit under the springs and generally stay in the body when you take out the pilot screws. Not know they are there, and blast some compressed air through the passages and they could have gone anywhere.

[Motorcyclelocksmith]

Jets sprayed and soaked in carb cleaner then compressed air. Set at 2 and a half then adjusted out 1 half per test. No parts lost

[Freddy]

Jets sprayed and soaked in carb cleaner then compressed air. Set at 2 and a half then adjusted out 1 half per test. No parts lost

When you say it won't idle, will it run at all if you don't spray petrol into the intake? Even if the pilot jets were still blocked (a possibility) I'd expect it to start on the choke and run if you keep the throttle open. You are using the choke to try and start it? Don't laugh, seems that generations raised only on fuel injected vehicles have no concept of using a choke and that you can't just immediate drive/ride away with a perfectly running engine.

Sticking with the basics first, have you primed the carbies? There is a prime position on the fuel tap (assuming its still fitted with the original tap). Turn the tap to the 'prime' position and leave it there till you have sorted out this problem. By doing so you've just eliminated a couple of potential problem areas.

With the tap now in the prime position, open each of the carby drain taps one at a time and check a solid flow of fuel coming from each. If you want to be safety conscious, put a short length of appropriate size plastic hose on the little 'spouts' near each drain screw and run the tube into a container. Much safer than pools of petrol laying on the floor where your working. Anyhow, this test will verify if all 4 carbies are getting fuel into them.

[Motorcyclelocksmith]

Only runs with fuel sprayed into intake. Choke on, open throttle, petcock on prime, and gas is in all 4 carbies

[Freddy]

Only runs with fuel sprayed into intake. Choke on, open throttle, petcock on prime, and gas is in all 4 carbies

Then the problem seemingly has to be in the carbies. Well at least I can think of nothing else.

I'd pull them apart again and clean each of the pilot jets (and mains) by running some suitable size nylon fishing line through the jets, pulled tight and rotating the jets around on it to scrape the inside of the jets. Alternative buy 4 new #35 genuine Kiehin pilot jets.

I've had jets partially blocked up internally that no amount of soaking in cleaner, ultrasonic cleaner, or compressed air would budge. You'd hold them up to the light and they'd look fine, but you couldn't tell they were way smaller than they should have been due to the rock hard buildup on the inside walls. For that reason I always scrape the insides of every jet in any carby I'm overhauling with the nylon fishing line method.

[Motorcyclelocksmith]

Ok thank you I will give it a try

[Freddy]

Ok thank you I will give it a try

What else can it be? When you're spraying petrol into the air box you're effectively duplicating the job of the pilot jets. I don't really know the internal passages in the carby that feed the enricher circuit, but you'd have to thing its also connected to the pilot jet somehow.

Don't know how you went about removing the carbies last time, but having done it quite a few times I come to the conclusion its easier overall to undo and remove extra things to make the job easier. This includes...

The coils
Regulator (this now gives way better access from above)
All the vacuum pipes (that statement related to non emissions pipes, no idea how in the road they are)
Disconnect the lower clutch cable and pull it up from between the carbies. Tuck that end out of the way somewhere.
Remove the 2 rubber blocks (one each side) on the sides of the air box. They sit at the back edge between the airbox and frame and position the airbox in the frame. Removing them allows you to pull the airbox back a little further. This extra 1/2" makes all the difference.
Pull the carbies out and up. There is way more space above the inlet manifolds than below to work the carby bank out the left hand side.

[Motorcyclelocksmith]

Carburetors professionaly gone over at repair shop and reinstalled.
No change