421 Alky Cub 35 PWKs

[Kendro]

To anyone who has run 35 PWKs on their 421 Alky Cub, My current set up is 35 PWK .125 dump .106 main 55 pilot. Have stock ignition and timing at +8. Bike runs 4.25 300 ft sand with 235 Rider. I strted at .120 main and worked my way down to .111 main only to find that i still could not run with power jets open at all. Now at .106 I can open clippard power jets 1 to 1 1/2 turns open and motor runs clean no detonation no signs of lean condition. Mixing Klotz Benol at 40:1

My questions are:

1. Is any one else running a main that small?

2. Is any one else running alky bikes with power jets full closed?

3. Is my main needing to be smaller than everyone else because of a larger dump than others? My thought process here is a larger air orifice ( dump tube) will pull more fuel through a given diameter fuel orifice because the suction will be stronger.

4. Is there a benefit in running power jets at say 4 turns out as opposed to 1 turn out.

5. Is anyone else mixing alky at 40:1? People say to run more oil 32:1 28:1 on alky but we are running more fuel through so arent we also running a lot more oil through at the same time.

I know this is a jetting related question but felt like the other drag racers would be best to ask.

Unfortunately I dont know anything about the port work as I bought it from previous owner but he said it only had clean up port job.

[sprinklerman]

Can't comment on all of what you're asking right now, but on the oil thing .... I ran my alky cubs on 20:1. For the simple reason thst cubs seem to like scuffing piston skirts ,especially on the intake side. Running lots of oil seems to have cured that (for me) as the last 3 Cub motors I had showed NO signs of scuffing since running 20:1. Dyno testing showed that 20:1 ( even richer that that ) didn't affect power. But the extra oil did help wear. A side benefit is 20:1 = 1qt oil to 5 gal fuel.

[SlowerThanYou]

To anyone who has run 35 PWKs on their 421 Alky Cub, My current set up is 35 PWK .125 dump .106 main 55 pilot. Have stock ignition and timing at +8. Bike runs 4.25 300 ft sand with 235 Rider. I strted at .120 main and worked my way down to .111 main only to find that i still could not run with power jets open at all. Now at .106 I can open clippard power jets 1 to 1 1/2 turns open and motor runs clean no detonation no signs of lean condition. Mixing Klotz Benol at 40:1

My questions are:

1. Is any one else running a main that small?

2. Is any one else running alky bikes with power jets full closed?

3. Is my main needing to be smaller than everyone else because of a larger dump than others? My thought process here is a larger air orifice ( dump tube) will pull more fuel through a given diameter fuel orifice because the suction will be stronger.

4. Is there a benefit in running power jets at say 4 turns out as opposed to 1 turn out.

5. Is anyone else mixing alky at 40:1? People say to run more oil 32:1 28:1 on alky but we are running more fuel through so arent we also running a lot more oil through at the same time.

I know this is a jetting related question but felt like the other drag racers would be best to ask.

Unfortunately I dont know anything about the port work as I bought it from previous owner but he said it only had clean up port job.

I had to go way back in our records to find some of your answers. The carbs were 35 PWKs with a .125 dump, never cared for that big of dump. We ran them on a 417 & 443 stock cylinder, & also on a 443 Cub.

 

Now, for your 1st question. We primarily ran mains in the .101 - .112 range & most of the time ran .104 - .108.

 

2nd ?: we always ran using a power jet with the above tunes. It wasn't a clippard style it was a Mikuni set-up with jets.

 

3rd ?: I'm pretty sure the small main is because of the large dump. Also, it seemed like we ran smaller pilot jets also around low - mid #40s.

 

4th ?: With a PWK, I prefer to let the carb do most of the fuel metering/atomization. To me the power jet dumps fuel in like a hose, but some mods can be done to better the atomization.

 

5th ?: As Sprinklerman gave a very good example of why you should run more oil in a cub. We ran 30:1 & had the wear problems on the intake.

 

These combos were ran on 1/8 & 1/4 mile asphalt.

 

[Kendro]

Thanks for replies im feeling better about not burning it down. I will start using more oil .

[dozer]

I would swap to 20:1 like the others said. Also the smaller carb( most run 39) will cause the motor to pull more fuel through the jet, there fore needing a smaller jet than a larger carb would.

[RadarRacing]

If you would like to lean the mid and top down a little it is easy with just a needle swap. Your dumps are quite big. It should have probably had about .116 dumps and .116mains and a needle in the EGN for duner/drag use or EGL range if you are a track only guy or use alot of timing in your setup. Then you would have been close to being able to use your powerjet for tuning a little. I would try some dgh needles in it with the .125 dumps and leaned out about 1 clip from the top and see if that gets you in a nice range to use your smaller mains like you have now but be good with a little PJ if needed. By the way there is no problem with running PJs all the way closed if they need leaned out more. Tuned 2 like that this weekend. I set my new pwks up last week so ot would be right in the middle and use 1.5 turns out on the PJ but can dump quite a bit more if needed. Hope that helps

Edited October 21, 2014 by RadarRacing