metalliman

Yeah, it won't hurt to try it, unfortunately I couldn't reuse mine. The needle had a groove wore all the way around, and it wouldn't seat properly, causing my carb to flood. You may have better luck though.

rotorhead

i used the 210 that came with my rebuild kit. i know it ain't perfect, but so far it runs well on my stock port 12a. i am certain it'll have to be changed by the time i get a streetport though. and yes, i've talked to that shop in the uk before, also nice and helpful, and they told me "we carry all parts made for the dellorto. when dellorto shut down, we bought out their warehouse." just expect it to be about 2 weeks for shipping if all goes well.

RXcetera

Nice to see the Dellorto is still very much alive and kicking on the Rotary scene. Spread the seeds of Dell knowledge Silver .

Metalliman, those pump jet weights are NOT part of the RB Dellorto setup. Also, 80-90 pumps are required to make the carb run hesitation free (and to keep you from running lean).

About your hesitation... The 3 most common causes of hesitation on a Dell: Badly sized/alligned pump jets, badly installed/adjusted mixture screws and a poorly adjusted throttle pump. If any one of these things isnt right, your carb will hesitate.

Rotor13B

Since the pump jet weights are gone, do the bearings that sit below them still need to be in there?

RXcetera

Yeah you still have to use the check ball bearings. They prevent gas/air from travelling back into the pump circuit through the jet when the pump goes from blow to suck (when you let off the throttle lol). Without the bearings, the throttle pump could also not fill properly causing stumbling (and other) problems.

You could use the weights if you wanted to, but the transition from blow to suck would be much more sudden causing, you guessed it... more stumbling.

Rotor13B

Well, I finally got my kit today, and the seat for the needle says 225 on it. According to gruntled.com, that is the largest they came with unless you got the viton tipped needle valve that is cross drilled(350). Is this gonna be acceptable, or should i look for a bigger needle and seat? btw, this is on a 13B.

Rotor13B

bump..

Rotor13B

Well, I got my carb kit installed and have the car running pretty good. There is one thing that 's bothering me though and that is when i first start it, it has a sortof stumble to it like it's not doing a complete burn of the fuel mixture, and cuts in and out for a few seconds and then finally come in running fine. Could this be caused by a high tension wire going bad or flooding? It has kind of a burbleing sound and as it gets better you can here it in the exhaust untill it gets its' throat cleared so to speak. Some helpfull hints from anyone would be appreciated.

metalliman

Well, this is what my car does. From idle at 1200 RPM (I have a street port) if I gradually give it gas, under no load, it stumbles up until about 2200 RPM. However, if I agressively hit the gas, it doesn't hesitate at all. This is what makes me think my idle jets are too small. By the way Rotor 13B, what size pump jets did you have in the carb?

RXcetera

Rotor13B, what you describe is perfectly normal when you start a cold sidedraft (and many other carbs). Try tapping the gas pedal a couple times before starting the engine... that helps a little. When the engine starts, let it idle at 2000rpm with the choke until it runs smoothly, then you're ready to go. It'll still be pretty choppy etc until the engine and carb fully warms up, so take it easy.

Metalliman, inspect your throttle pump mechanism to make sure it's working smoothly. Take the carb off and visualy see if the jet from the pump is consistent when slowly applying throttle. If that checks out, try readjusting your mixture screws some more.

Rotor13B

Metalliman, I have the #80 pump jets in my carb, same as from RB. I don't understand why the 12a dells have the #90 pump jets and the 13B dells have the 80's, you would think that it would be the other way around.

metalliman

I guess that would make my little #60 pump jets way too small. It's funny I don't have any hesitation under WOT.

RXcetera

RB started with #80 pump jets in both 12A and 13B carbs, then switched to #90 pumps later in production. They both work fine for both applications, but I've always found the #90 to be smoother at the expense of mileage.

#60 IS way too small. How can I explain this... ok... The whole accelerator pump circuit works similarily to a water gun. Think of the pump jet as the tip at the end of the gun and the throttle pump as the trigger. When you depress the throttle, it depresses the pump (trigger) and gas squirts out the pump jet (tip). Just like a water gun, after a few seconds gas will stop squirting... the only way to get more fuel out is to release the throttle and push it again. Make sense? If you're at WOT for more than a couple seconds, your throttle pump and pump jets dont do anything anymore.

Now, if you change the size of the tip on the water gun to say, a smaller one, the result will be: Less water coming out the gun at one time, but the water will come out for a longer period for each pump right? The same is true for a bigger tip... more water coming out but a shorter squirt. Applying this knowledge to your carb now... #60 pump jets are small. That means, when partially applying the throttle, you arent putting enough gas in the engine at any one time to richen up the mixture to the point of avoiding stumble. The only way you could prevent stumbling would be to floor the throttle to WOT and hope that the full stoke of the throttle pump and the longer duration of the stroke would be enough fuel for the engine. In your case, that appears to be what is happening. Put a bigger pump jet in there, and you'll be dumping more fuel in the engine at any one time, no matter how much throttle you apply. That should cure your stumbling.

If that doesnt do it, the problem could be the actual "trigger". If the throttle pump itself isnt working properly, it could have the same effect as being hesitant when pressing your water gun trigger. Gas will dribble out sporaticaly out of the jets, but you'll never get a good clean stroke.

This stuff is really simple when you sit down and think about it... but even before trying to understand it you NEED to get the proper jets for you carb. There's no point in "trying" to get it to run well with improper jetting because it WONT WORK. These carbs ARE an exact science (all carbs are lol) and everything has to functioning properly to acheive good results. If you cant adopt this "no shortcuts" kind of mentality when setting up your Dellorto, you'll never get it to run right.