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Author Topic:   carb. help
02racing
Member
posted April 05, 2004 09:36 AM
Running 377 on alky with roller cam 630 630 lift with dart 215cc heads fully ported and nascar valve job 13.5 to 1 compression with matched 360 intake with 750 B.G. carb need help on powervalve size and jets we have a 65 in now with 88-89 jets running 180 degrees on track but still have a miss when you try to stand on it hard. Squirters are 28 not sure whether I should change squirter size or lean down more plugs look pretty close. Thanks for any help.

[This message has been edited by 02racing (edited April 05, 2004).]

KPLugnut
Member
posted April 05, 2004 01:45 PM
those squirter sizes are for gas carbs. alky carbs use .037 or larger (ours are 45's, usually).
With squirters that small on alky, you're not filling the flat spot when the pumps are activated and there is your hesitation....at least that's the first place to fix anyway.
There could be other problems, too, but without actually seeing the carb, that's all I can tell ya for starters.

The jetting may actually be a bit on the low side, but it depends what size holes BG drilled in the metering blocks. The power valve is fine. The only real way to figure the jetting is to flow the carb, or at the very least calculate the total jet area you've got, and see if that matches what the carb has for venturi diameter and throttle bore (at least that'll get ya in the ballpark).
Air quality, air temp, humidity, and engine specs (compression, etc etc) all will factor into final jet size)

Hope that helps,
KP

[This message has been edited by KPLugnut (edited April 05, 2004).]

juliaferrell
Member
posted April 06, 2004 10:20 AM
Another quick carb tuning tip is if the engine stumbles in the garage during free rev take your hand and restrict the air going into the carb and see if this helps your stumble. I take a flat metal plate and slowly slide over the opening a little at a time and listen. Stumbling on alky usually always means lean. Just get your jet assortment and cam assortments and tune.
I LOVE DYNOS!!!


02racing
Member
posted April 06, 2004 04:42 PM
It does not stumble in the garage it is super crisp and very responsive. The jets look good according to the plugs. We checked the after hot laps I shut it off after 4 laps and wide open down front straight and rolled in. I think we will put the 45 squirters in and try that. We had 28 in because thats what several people at the track are running and told us to try last year when we had a bad miss. Last year it turned out to be valve springs but this miss is different it feels like carb. Last year felt like floating the valves.


juliaferrell
Member
posted April 06, 2004 05:36 PM
If I weren't confident that I fixed the problem at the garage. I would definately restrict a portion of the carb during hot laps if I thought the condition was still there. You definately need 43 plus squirter. **Remember: None run lean on alky long before they pop!! I'd make darn sure I went the other way. I'd check that needle and seat too.


02racing
Member
posted April 12, 2004 08:15 AM
We went tou this weekend and put the 65 powervalve in and 45 squirters and it did the same thing we had some help from another drivers motor guy come over and he also was baffled at what it was doing he used his temp gun and checkek bank temps and said they were perfect. Also thought the plugs looked good. So we ran our feature and the problem was gone for about 5 laps then started in again and got worse and worse till the end of the feature temp was 180 and never came off of 180. He said the only thing he could see that might cause the problem is our return hose is to small and the longer we run under green the more pressure we are building up because it can't return all the alky. We run a 6an hose and a rons belt drive pump. Also under caution we would restart and it would be ok for a lap or two. Since putting those 45 squirters in though it falls flat on its face when you flat foot it on starts. We ruled out ignition and timing those where two things we tried saturday getting very frustrated with this miss any help is appreciated.


02racing
Member
posted April 12, 2004 08:23 AM
Also the tops of the pistons look like their coated with top lube from the alky. Thats why he said return hose backing up pressure the making it run over.


autoshop
Member
posted April 12, 2004 10:05 AM
With that big of cam I would check to see if the power valves are not to big of number (6.5)
I bet if you put a vacumn gauge you only have 7 inches of vacumn and need to use a 3.5 valve instead of the 6.5 .I run a BG and my jets are 92 and 94 but then again I run my motors fat.I also block off about half my radaitor and run the motor at 195 to 200.


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