Running a stock rebuild (refresh) of a '69 455 Toro motor with a rebuilt L69 set up. The carbs were rebuilt to factory specs. Having a hard time getting the idle below 1100 RPM without stalling.

Ran fine with a 750 and HEI. Less than 50 miles on the refresh. Then, a new street strip distributor, a multi-spark box, new tank and new fuel pump.

Running 93 octane with lead additive after the tank install, but the same was happening when using AV/100 gas before the new pump and tank.

Does this sound like a jetting issue?

 

The outer carbs should be "dead" at idle. I'd make sure those are doing nothing first (just cover the air horns) then if that shows nothing then I'd start looking for vacuum leaks. If still nothing then it sounds like you have an issue with the center carb.

 

Just picked up a vacume guage to check it. Haven't had a chance to test it yet. Thanks for the help!

The increased size of the motor concerns me with the jetting. Anybody using the L69 on a 455?

 

I am sure many folks have done that. I have one but haven't run it yet so I can't say specifically how it'll work.

I can say, though, that "jetting" has little or nothing to do with idle. The Idle fuel comes thru, well, the idle passages... and past the adjustment needles. While that fuel may well come thru the main jets, the flow would be so very low that the size of the jet should have no effect on that flow. You should read up on the operation of the 6 basic carb systems in play on the center carb.

Make sure the front and back carbs are totally closed at idle. Disconnect/ plug all other possible vacuum leaks. Ck for leaks around the carb base to intake using the usual spray of flammable juice or stream of propane or whatnot. I have seen factory 2-bbl carbs assembled with intentional? LEAKS in the base to body gaskets. By the factory. One was an NOS carb. These leaks however are above the throttle plates and so other than letting in dirty air, they should not affect the flow of idle air and fuel. IT couldn't hurt to open the center carb and probe all the idle fuel passages, ensure the proper gasket is there, with a hole to pass the idle fuel...

Is your timing advanced enough? I could not get my 403 QJet to idle when the timing was too retarded, due to the greatly increased compression and more radical cam. It would stumble-idle at like 1100, then just die off below that. Advancing the timing got good idle but detonation in the mid and upper RPM's, so that led to adjustments to the HEI's vacuum and mechanical advance curves.

 

Ugh! My big plans of pulling her out of storage to play this weekend are crushed by rain! Maybe next weekend.

 

That not fun when you work all week to look forward to driving the toys on the weekend and it rains! I know it well living in the northeast. For once we have a stretch of good weather, I already put 200 miles on my 70 this week. I also have been on vacay this week too. Good luck on the fix and better weather will come. You will be able to drive your car long after mines put to bed for winter!

 

The AL and AU castings of the Tri-Carb intake could leak vacuum at the center carb base. Olds put out a service bulletin to use Permatex #1 to help seal the center carb base gasket. The real problem is that it is unsupported by the manifold pad outboard of the vacuum passage in the carb base. The AZ casting fixed the problem with a bigger base pad for the center carb. The end carbs don't have the problematic base vacuum recess and are OK with the smaller pads.

 

Good info! THANKS!

 

Spray of flammable stuff or propane waft should find any such vacuum leaks easily.

 

Planning on trying the propane test. Makes me cringe to spray flammable liquid on a freshly painted intake.
455andtri-carb.jpg

 

You have many good suggestions. Often the problem is that the end carburetors do not seal tight when closed. If the suggestions you have do not resolve the problem you can replace the end carburetors with block off plates and then get the engine to run correctly on just the center carburetor. After this is done put back the end carburetors one at a time and see if things degrade again. If so, concentrate on the offending carburetor(s). Sometimes a heavier return spring may help. Sometimes the DAG treatment of the throttle bores may resolve the situation. Try to shine a light through the throttle body assemblies when they are removed from the rest of the carburetor. No light should be seen. There is a bit of a price to pay to have a well performing L69.