XR4 idle mixture adjustment for smoother idle?

Anyone know if the carbs on a 1988 XR4 V-6 have any sort of adjustment for smoothing the idle on each carb? Motor starts good and runs like a son of a gun at wide open throttle but the idle doesn't seem smooth or sound right. Seems to be bucking as if missing at idle and just off idle. Maybe one of the 2 control modules is acting up, or the idle stabilizer module? Any advice would be appreciated. First year running the motor so haven't rebuilt the carbs yet but will this winter.
Thanks Wayne

Re: XR4 idle mixture adjustment for smoother idle?

Link and sync is critical on the XR4, as in all V6's. There is no idle mixture adjustment. It is preset with the jets. It is plenty fat for smooth idle.

Bleed lines and bleed check valves are also critical to good idle.

I got the last of the smoothness in my engine by changing the stock steel reed valves for Chris Carson fiberglass reed valves. They are more sensitive and nimble, and do wonders for the idle.

The original carbs are either WH41 or WH41A. The 41's idle jet is .052. The 41A is .048. If it's pig rich at idle, you could try the larger idle jets. (larger is leaner)

hope it helps
John

Re: XR4 idle mixture adjustment for smoother idle?

Thanks John. I was hoping you would chime in since you run an XR4. I did notice the middle right cylinder was black with oil while idleing on muffs but after running it on the lake all plugs seemed OK. Compression was even on all cylinders. It does smoke a lot when you first start it after sitting but once warm it is ok. Oil pump is on the mark. I have a set of carbs from a Mariner Magnum II that look the same so I may try rebuilding those and switching them out to see if there is any difference. Just doesn't seem smooth at idle or part throttle. It's a gas hog but runs very strong at full throttle. Do you know the timing for the link and sync off hand. Idle timing, timing where it first hits the throttle, and full throttle timing. Can't seem to find my merc manual.
Thanks Wayne

Re: XR4 idle mixture adjustment for smoother idle?

Mag II and XR4 are the same animal. either could have 41 or 41A carbs on them. Probably the only difference is the idle air jet. Could be a difference in the idle circuit internally, but I doubt it.

Before you get too carried away, check the bleed lines and bleed check valves. That's classic for a stuck bleed valve or split line. (one dirty plug after idle)

Idle stop screw ---> Throttle cam 1/8" off stop.
Throttle roller ---> just touching the throttle cam (sometimes we back that off 1/8" if off idle bogs)
Throttle pickup (primary) ---> 11? ATDC
WOT timing ---> 18? BTDC with advance module. 22? without.
Max throttle stop ---> .010-.015 clearance roller to cam at WOT

hope it helps
john

Re: XR4 idle mixture adjustment for smoother idle?

Thanks John. By bleed lines do you mean the tiny black tubing coming from each carb to the block? If so where are the check valves located? Would the black plug be the one to check closest? Finally where do you buy that tubing. I had the 1973 inline 6 1500 purring like a kitten till I came across the XR4 and sold it. Now I have to start learning all over again. The XR4 has way more power though.
Wayne

Re: XR4 idle mixture adjustment for smoother idle?

On a vert front engine, the check valves are directly in front of each cylinder, so the possibly errant one would be #3, just in front of the dirty plug. The check valve should flow out (into the tubing) but not the other way. The tube from that one should go to #6, or bottom port cylinder.

Merc has a part #. Tygon small engine hose will work. Any merc shop should have a roll around to sell you some.

hope it helps
John

Re: XR4 idle mixture adjustment for smoother idle?

I think I saw where they go into the block just in front of the head. Can they be cleaned if bad or do you just replace them? Boat is at the lake so I'll check them and the hoses next time I go up. Thanks for the help.
Wayne