Linkert stumbling

[Weston1955]

Hey guys, forgive me if this has been discussed before but I was unable to find a thread on iT.
I'm having a bit of a problem with my linkert stumbling after shifting gears. For example I'll be at the top of second gear and it's running fine but as soon as I shift in to third it stumbles and I have to twist the throttle a few times to get it to even out and catch up. It happens through all the gears. It seems to be getting pretty poor gas mileage as well ( about 35 mpg on a stripped down chopper) plugs were really black and sooty and I tuned the high speed needle all the way in and now the plugs look better but it still stumbles. Any help would be greatly appreciated.

[Bigincher]

First, you will want to 'bubble test' the intake tract by removing the carb, fashioning a block-off plate with a fitting to introduce 10-15 psi, while squirting a soapy water solution around the connections of the intake manifold, be it rubber o-rings or compression seals. If there are any bubbles present, no matter how small, you must rectify the issue and test again until there are no bubbles. There is no shortcut to the bubble test.
After that, if the performance doesn't improve, you will want to look within the carburetor, starting with the float, which might not be floating. Also check throttle shaft in its bushing, and let's not forget to clean or replace the air filter.

[Weston1955]

Got the bubble test done this evening and everything checked out great. It's got the o ring intake and I couldn't detect any leaks through there. Next step is to check the float inside the carb and go from there. I actually got one of cottons floats a few weeks back so this is the perfect time to install it and check everything. Is the 19 jet too big perhaps? Thanks so much for your help, I truly appreciate it

[Weston1955]

Also, upon inspection this evening I discovered the Venturi was pretty loose. Enough so that I can see daylight around it and it slides right out once the nozzle it removed. Could that be causing the symptoms I described?

[Bigincher]

The 19 is stock size on an M74B. The loose venturi would certainly make it difficult to tune, for sure.
There's a way to correct that, you need the right tool, a large cone-shaped 'anvil' that is placed inside the venturi then whacked with a hammer, 'swedging' it to cause the OD to increase. (Not the best explanation, hope you get the idea). I think that process requires the right tool, a little experience, and just the right touch. Maybe you can send it out and have it done in a reasonable time.
What kind of element are you using in the air filter?

[Weston1955]

Thanks for the info. I'll try to source that job out since it sounds like a delicate process and something that can very easily be overdone.
I've been running a bird deflector on it as of late but have a round copper mesh filter that I was going to instal as well to see if that does anything for tuning ability. Does anyone make a "good" replacement Venturi? I heard colony changed their process and they are somewhat better now .

[RUBONE]

The best replacement venturis are custom made to fit individual carbs. Usually only done by well versed tuners. The factory potmetal types tend to shrink over time and loosen. Be sure to check the washer under the low speed spring to be sure it is there and positioned correctly. Also throttle disc to body fit. And make sure the main nozzle is all the way up and seated in the venturi as well. The 35 MPG is fairly typical of Linkert mileage so that in itself isn't a good indicator of issues. The plug reading is though. And don't forget on the bubble test to check the head casting around the ports as well as the nipples and manifold connections, down between the fins where other features are close to the ports.

[v2panhead74]

Weston,
Was the culprit a loose Venturi?

[Buddhahoodvatoloco]

Trailer ball will work..............

The 19 is stock size on an M74B. The loose venturi would certainly make it difficult to tune, for sure.
There's a way to correct that, you need the right tool, a large cone-shaped 'anvil' that is placed inside the venturi then whacked with a hammer, 'swedging' it to cause the OD to increase. (Not the best explanation, hope you get the idea). I think that process requires the right tool, a little experience, and just the right touch. Maybe you can send it out and have it done in a reasonable time.
What kind of element are you using in the air filter?

[Bigincher]

Trailer ball will work..............

Cool, good to know..!

[Buddhahoodvatoloco]

A real Linkert stud muffin taught me that, but size your "Balls" first.