Mikuni PHH adjustment question

[EricB]

So I finally got my own synchrometer (SKtype) and after having warmed up the engine and disconnected the throttle arms from the throttle shafts I took some baseline readings...

The gauge on the synchrometer goes from 0 to 30.

Both barrels on the first carb (the one closest to the front of the car) showed a value of 6 on the gauge, while the remaining four barrels on the other two carbs all registered at 3.25 to 3.5

The synchrometer manual/leaflet indicated that before any tuning could be done all carbs need to be within one gradation of one another... Obviously this is not the case here...

On the other hand though my stock NGK BP6ES plugs look fine, I've got an O2 sensor plumbed just rearward of the header collector which is showing barely a tick over stoichometric so that's good too... Am getting great power and torque and even better MPG on the freeway...

The Mikunis don't have that many adjustment features unlike Weber DCOEs for example and all three carbs have their idle mixture adjustment screws set at 2.5 turns out from seated as indicated in the Mikuni manual.

So what can I adjust?

Where would this discrepancy come from?

Any ideas or suggestions?

Thanks all & it's good to be back - yeah!

-e

[gramercyjam]

You wouldn't be adjusting mixture with a syncronmeter, just syncronizing the throttle plates for even air flow across the carbs.

[EricB]

Yes of course I realize that... I was just stating that I've got the PHH setup as indicated by the factory manual and wondering out loud HOW to adjust airflow on a carb which doesn't really have many provisions for adjustment... know what I mean?

[Victor Laury]

Several different Mikuni PHH series have different throttle stop arrangements for idle speed adjustment. None are cast in the carb assembly, but fastened to the sides with screws and limits the rest point of the throttle arm. If you have none, do you have turn buckle style throttle pull rods? those "can" be used to balance the idle speed of each carb, but it's not ideal as the main rod will twists and not always comes to rest at the same point.

[Victor Laury]

Eric, Found a diagram showing the throttle stop screw and fittings of a 44 PHH, of the "Late" series (single screw jet cover)

44 PHH

Notice items 37 ~ 41

[gramercyjam]

Yes of course I realize that...

Sorry, I wasn't sure since there was mention of plugs and an O2 sensor. My own experience with syncrometers hasn't been good. I prefer to measure the amount each throttle plate is open at idle and listen to the carbs.

[EricB]

Hmm... ok... I'll spend some more time on them this weekend and report back...

Victor that picture you posted leads me to another question, in the exploded view check out part #85 which is listed as "Cooling Body Assembly"... What is that? Mine came with it, I've got nozzles plugged off because I didn't know what they were... but "cooling assembly"???? For cooling the fuel in the bowl because the carb sits above the header??? What would one route through there to cool the fuel???

-e

[Victor Laury]

Eric, I have them too on my set of 44's on the roadster. I have them open, attached to nothing.

[Tyrone]

Was just wondering if any of you can tell me how I would go about adjusting my fuel pilot screw on my 44PHH mikuni's?

[jmortensen]

Turn them all in until they hit the stops (gently, don't mash them into the stops). Then back them all out 1.5 turns. You're now adjusted. If it's too lean, get a bigger pilot jet. Too rich, get a smaller pilot jet.

Some people go 1.25 turns with the above method. Either way, the idea is that the pilot has a function over a fairly large rpm range and cranking the screw open to change the performance at idle leaves you with a lean spot a bit higher up.

[five&dime]

My twin 44's had slightly different readings similar to this as well. The adjustment needed was at the idle stop plate adjustment screw. I don't know if this is what you need just trying to help. They needed to have the same idle stop placement before the individual adjustment screws were synced.

I think the first two ended up being around 1 1/2 turns and the rear two were at 2 turns.

Edited May 22, 2009 by five&dime

[jmortensen]

My twin 44's had slightly different readings similar to this as well. The adjustment needed was at the idle stop plate adjustment screw. I don't know if this is what you need just trying to help. They needed to have the same idle stop placement before the individual adjustment screws were synced.

I think the first two ended up being around 1 1/2 turns and the rear two were at 2 turns.

Are you answering the question from today or 2004?