View Full Version : Mixture adjustment on Strombergs

07-29-2009, 09:54 PM
I have adjustable Strombergs on my TR250 and was planning to use my color tune to make some finer adjustments. I took a brief look through my manuals and did not see what direction to turn the adjuster to chance the mixture. So witch direction to lean it out?

07-29-2009, 10:07 PM
Clockwise = richer. You're turning a screw into a nut attached to the needle, so turning the screw "in" raises the needle for a richer mixture.

Don't forget, that screw is brass (hence relatively soft) and has a limited range. Don't force it. And if you back the screw out of the threads, most likely you'll have to remove the piston to push the needle carrier back in and engage the threads.

07-29-2009, 11:30 PM
Thanks! I thought about taking the pistons out first then cleaning and testing the needle screw. Figure it would make things a little easier because the first time I tried it they were very stiff. I'm sure the rubber diaphragms can tear easily.

07-30-2009, 06:45 AM
If you have never rebuilt these carbs they are actually pretty easy to do, and it makes a big difference. If all she needs is some tweaking then no need to rebuild, but if you aren't sure how long it has been since it was last done I'd recommend you consider doing it. I just did mine and I found lots of issues and differences between the two carbs on the bits inside them...

07-30-2009, 08:11 AM
Randall warned you about the needle loosing contact with the adjusting screw threads. From fully Clockwise (rich) until fully Counterclockwise is a bit less than 3 turns. Call it 2 1/2 to be safe.
What I like to do is turn the screw fully CW, then CCW 1 1/2 as a starting point.
When I encounter diffficulty turning the screw, I take the air valve out, just to see the needles location and because it is safer and easier than trying to hold the adjuster when excessive torque is needed to turn the screw.
Sometimes it's the "star washer" that has gotten cockeyed thats creating the resistance.

07-30-2009, 08:40 AM
Between Randall and Poolboy you are <span style="text-decoration: underline">very</span> well supported here....

Keep us posted on how it goes!

Geo Hahn
07-30-2009, 05:20 PM
Clockwise = richer...

My easy way to remember this is (viewed from above):

Right = Richer

Left = Leaner

I like no-brainer systems when possible.

07-30-2009, 07:09 PM
Right = Richer

Left = Leaner

I like that! Reminds me of my boating classes. "Red Right Return". That's how my mind works. Now with age creeping up; how does that word association go?

Any way the carbs were rebuilt 9k ago. All 3 of them. Originally did an ear tune and checked the plugs. Now that I have the color tune it should be quite easy.

Just did the TR3 a few days ago and easy to dial in. Had to richen it up a bit twice after test driving. Spot on now. I'll be able to check mpg on the trip to TRF party almost 3 hours away. Looking forward to a good time. Taking both cars along with my son and daughter. This will be her first time to race. Look out Danica!

08-02-2009, 11:54 PM
Keep us posted on how it goes!

I'll do this monday. Worked around the clock since Fri night on both cars and still not done. 250 tume up turned out great!

08-04-2009, 07:40 PM
TDSKIP asked to be updated. Well this worked out as well as the TR3. She runs the smoothest ever. I first balanced the carbs then bumped the idle to 1000 rmp. Then I checked # 2 cylinder. Could not get the color tune plug into #1 because the alternator is in the way. Doesn't matter as long as the carb you are adjusting is feeding that cylinder. It was very rich. Took a lot of turns to get it to indigo blue.

The middle carb was a little better but found out why the knurled top is on the guide. Holding it between your thumb and forfinger it keeps the piston from turning while adjusting the needle. I went as far as I could to lean it out. Could only get to blue with a yellow tick to the flame.

The rear carb was spot on and no adjustment there.

Re-balanced the carbs. It did change the balance and it runs very smooth. Even idles at 800 rpms with a mild street cam with 155:1 rockers.
Fresh plugs, good rebuilt carbs and a excellent tune job = smooooth running car! Can't wait to make the 3 hour tour to TRF.