low RPM at full throttle

[turboturner]

again...
I ran the engine (912UL) for the 1st time since changing the carb flange which had cracked (right carb - cyl 1 & 3). The problem persists: max 4800 RPM (vs 5200) with engine running rough at most RPMs (sometimes smooth). What I checked so far:
- all plugs removed, cleaned. The two on cyl 2 were covered in black soot. All gaps good.
- carb bowls inspected. Both were clean;
- carb sync appears OK (eyeball);
- carb adjustment ok (1½ turn);
- compression chk (not the differential method, just "straight"). All above 95;
- bad gas? drained tanks & used recent 92 octane.
Has anyone ever had this problem?
Thnx for any info.

[HighWing]

Based on the plug apprearance on cylinder 2, my guess is that you have an ignition problem most - likely a broken wire in the ignition module bundle. This is another reason for moving the module from the engine to the firewall as this is not that uncommon. As a friend - an aerospace engneer - once said, the Rotax wire in the module is "crap wire".

From the reports I have heard, there are two ways to check the wires. Try stretching each wire to see if one lengthens with the stretch and the other is to use sewing needles to penetrate the insulation so an ohmmeter can be used to check for a break. It is not advised to check for the spark by removing a plug as I understand that an ungrounded plug can fry the $900 module. We were able to do the fix on a remote location once because one of the guys had a propane soldering iron.

Lowell

Hope it is a simple fi

[Dorsal]

The "sometimes smooth" would also support a broken wire,the connection may be made and broken with movement and heat.

[turboturner]

problem solved - carbs were out-of-sync. Mechanically, they appeared in sync, but it doesn't take much. I discovered this by pushing alternatively on one of the two cables leading from the "throttle bar" (under the dash) to each carb, while the engine was running. It was thus possible to sync the carbs temporarily with a simple push. I synchronized them permanently using the cable adjustment on the carbs (but need to do it properly w/ vacuum gauges).
The reason they were out-of-sync was that the nut holding the cable to the right carb was just loose enough to allow the cable to slip out, slightly but progressively. Did a lot of investigating before finding this out - a learning experience. It's easy to assume the worse.
Thank you again for your advice.

[DanB]

problem solved - carbs were out-of-sync. Mechanically, they appeared in sync, but it doesn't take much. I discovered this by pushing alternatively on one of the two cables leading from the "throttle bar" (under the dash) to each carb, while the engine was running. It was thus possible to sync the carbs temporarily with a simple push. I synchronized them permanently using the cable adjustment on the carbs (but need to do it properly w/ vacuum gauges).
The reason they were out-of-sync was that the nut holding the cable to the right carb was just loose enough to allow the cable to slip out, slightly but progressively. Did a lot of investigating before finding this out - a learning experience. It's easy to assume the worse.
Thank you again for your advice.

Turbo,
Thanks for the update... glad you found the problem.

[cap01]

turbo , awhile back i installed a throttle link from highwing llc . with this installed you can sync the carbs from the cockpit without loosening any of the throttle cable nuts . at first i thought the $49.00 it cost was pretty high but after using it , i see its well worth the price . it takes longer to wait for the engine to get up to temp than to sync the carbs with this thing installed . it only will work with the belcrank type throttles but thats what i have .
http://www.highwingllc.com/throttlelink.html (http://www.highwingllc.com/throttlelink.html)

[catz631]

I have had the throttle link installed for over 2 years now and no way would I be without it. I can pneumaticaly sync the carbs in about a minute (again after warm up) using the throttle link and Twin Max carb sync instrument. Thanks again for that fine invention Lowell !
Dick

[Av8r3400]

Can anyone give a photo of one of these installed? Carb-syncing seems to be a constant battle on my plane...

[HighWing]

Throttle Link

[Av8r3400]

OOOOkay... Now I get it. :)

Does this adjuster kit come with a longer cable core? The ones I have are **just** long enough to reach.

[cap01]

yes , it comes with a longer cable