Synchronize Throttle Control

[C-Sick]

I just took my 22ft twin honda 40 out after having it tuned at the factory. The throttle controls at the helm when lined up evenly are at different rpms. (Off by 200- 300) Is there a simple adjustment for this or will I need to trail it back to the factory.

[Captains Cat]

I've got the same problem with twin 45's (1994 hondas). I'm pretty sure there's an adjustment on a cable under the engine covers. I'll look in my service manual (the big one) later and let you know if I find anything.

Charlie

[Les Lampman]

Hey Ya'll...

The adjustment on the Honda BF40/50's is under the motor hood (well, there's one inside the remote control too but that's much more of a pain). Pull the hood off and stand (this is easier on land ) on the starboard side of the engine looking at the magnificent beast. One of the larger masses (just ahead of the carbs) is the black plastic air intake assembly. Once you've identified that look just under the lower edge and you'll see where the throttle cable connects to the throttle arm. To verify you're in the right place; look farther forward to where you can see the two control cables coming into the engine housing then follow them back; the cable toward the inside of the engine is the shift cable and the outer one is throttle.

You need to decide which engine to adjust to match the other; I do this by looking at the length of the threads sticking out of the Pivot Pin (the brass thing threaded onto the throttle cable that sticks through the throttle arm of the engine). The throttle cable PULLS forward to increase rpm so that means to raise the rpm to match the other engine you thread the pivot pin farther onto the cable end; if you're out of threads this won't work so that means you need to lower rpm on the other engine by unthreading the pivot pin on the cable end.

Keep reading before you try this The pin on the pivot pin (that goes through the hole on the engine's throttle arm) points IN toward the center of the engine (if it points out it can bind the cable). Also, there should be two flat stainless washers on the pivot pin; one goes on the outside of the throttle arm and the other on the inside. These form bearing surfaces (the throttle arm is plastic) and should absolutely be used. So, the order of things on the pivot pin (from outside to inside) is a flat washer, then the pin goes through the arm, then the inner flat washer gets put on, and then the hairpin clip gets inserted in its hole at the end of the pin.

Some tips: Have some good waterproof grease handy and a pair of needlenose pliers or hemostats close by too. Reach in with the pliers and pull straight up on the hairpin clip to remove it and hold the outside of the pivot bolt so it stays in the throttle arm. Now, before you pull the pivot bolt out reach in with your right forefinger and put it on the inboard end of the pivot pin. Now as you gently pull the pivot pin toward you capture the flat washer on the inside of the throttle arm with your finger (a dab of grease on the end of your finger works good) and DON'T DROP IT! The outer washer will stay on the pivot pin (usually ). Now you can thread or unthread the pivot pin as necessary; try 2 to 4 turns at a time until you get it right. When you put things back together use plenty of grease to keep the flat washers under control and make sure you end up with the pivot pin pointing into the engine. I usually do this on the water during sea trials so while it sounds trickly it's not Mission Impossible (I use the pliers on my Swiss Army Knife ).

I've never been able to get the throttle 100% synchronized at all speeds (we're dealing with a mechanical system with too many variables and too much slop) so I try to get them working well in the normal cruise range. If the cables are set up correctly getting even idle speeds is done with the idle adjustment screws; cable adjustment should not come into play at all at idle.

I might also point out that you've got six carberators involved; maintaining even throttles also supposses that the carbs are synchronized and in good working order. So if things have been good and then change it's usually carb sync rather than a mechanical issue.

This is easier to do than to write about; hopefully this will make sense once you look at your engines!

[C-Sick]

Les & Charlie,

Thanks for your input. They worked fine before the tune up so I am hoping a simple adjustment will work. I did a visual on them to today. The number of exposed threads is equal on both of them and there is room for adjustment. I going to wait until I take it out again to both check the idle and to see at what crusing speed I have the greatest variation.

[Captains Cat]

I don't know why we bother with service manuals when we've got Les!!

Thanks, it's a better explanation than Honda gives and probably more accurate too!!

Charlie

[Chuck S]

Good luck on getting the engines synced!

We had vernier controlls on the older light twin aircraft which could make very fine throttle changes vs. the gross changes in the main throttles. As Les notes you're moving the throttles on 3 carbs per engine.

Harmonics will drive some folks nuts. I'd think there'd be a market for this sort of control for twin outboards in this class. There are exotic electronics which will keep the engines in sync, but I've not looked at them close enough to see if they have any chance of being adopted to the Hondas. "Fly by wire" this ain't!

-- Chuck

[Butch]

Great thread! and good advice!
You all made up my mind about twin or single power plants. The issue before this thread for me was weight and now that I have heard from the masses... single is the way I will go on the 25 CD.
Thanks you all! Butch

[CAVU]

Yes this turned out to be a very timely thread for me. I had just installed new throttle and shift cables on my 90HP Honda. After reading this thread, I checked my throttle cable linkage and discovered I had left the washers off somehow. Easily corrected. Thanks Les.

[Les Lampman]

There are a couple of other things I should mention...1) there is a certain amount of mechanical play in the cable system. If you grab a hold of the cable end (when disconnected from the engine) you can move the inner cable in and out of the outer cable sheath a few fractions of an inch. It's enough so that if one cable is 'pushed' all the way in when set for idle and the other (on the other twin) is 'pulled' all the way out when set at idle the throttles won't line up. Both cables need to be setup the same way...I prefer to 'push' them in to get slack out. [The Honda's use pull-to-open throttles. With the slack taken out by pushing the inner cable in, we'll get more a more consistent idle position on the throttle cam when the cable 'pushes' back to idle.]

2) When setting the idle (or initial position) of the throttle cable pivot pin (with the remote control in neutral) you're kind of setting things in 'mid-air' since the throttle cam is not pushed or pulled up against anything.

To set the scene: if you look at the bottom of the carb stack you'll see a round brass pin running in a slot in the black plastic throttle cam (to which is attached a stainless rod running forward to the throttle arm where the cable is connected).

On the black plastic throttle cam you'll find a vertical mark molded in. When the pivot pin on the throttle cable end is adjusted properly a line extend below the molded-in mark should bisect the round brass pin in the slot (which is attached to pickup arm on the carb it self) with the remote control in neutral (at idle). There will be some open space in the slot on the forward side (and a bunch on the aft side); I've often found that all the 'slack' was taken out of the slot (toward the forward end); if so, that means you can't get always get full throttle. Since the brass pin is much wider than the molded mark, lining it up is a matter of personal interpretation. A few fractions either way won't make any difference but with twins it helps if they are both set up the same initially; then you can deviate a bit to balance the throttle levers for cruise speeds.