604 Carb

[RacerX10]

I tried my Race Demon 750 carb on my new 604 last night, and it's not running well off the corners. Slow wrap up, burbling a little, etc. It got better as the night got cooler, but it's still not right.

Jets are 76 front 77 rear.

Is this fixable via tuning or do I need a new carb ?

If I need a new carb, what's the least expensive route to go that works well. I don't care about making an extra 15 HP with a $1,250 tuned carb. I just want something that works.

Related question : when people are selling what looks like a stock holly carb with some anodized parts on it as "race tuned", what exactly have they done to it ?

Thanks.

[pcope98]

you have way to much jet in it i had a 71's in mine to make it work but your carb will be no match to a good willys or stealth trust me i fought with several carbs and bought a willeys and havent ever had a problem since then and the power is much better with a real tuned carb not some ebay special

[RacerX10]

Thanks for the reply !

I was told 75's were "stock" front and rear in that motor, and the guy I bought the motor from said he had 76's in his.

Hard to get good info on this deal

You think 71's front and rear will make it usable (for now) ? I'm planning on skipping a race tomorrow night cause it's not running well as is.

I've been googling around and it seems like some crate carb venders are using 750's, and some are using 650's .. so confusing.

It also looks to me like they only thing they are changing is the metering blocks .. is that the case ?

Oh yeah, what about the power valve ? I think it's got 3.5's in it right now.

[Matt49]

Cooler air is denser air so the fact that it got better as air temps cooled is an indication that you are running too rich. I would say that is way too much jetting for that motor but that can very based on where you are. Your bowl levels could be too high or you could have too much fuel pressure which makes the bowls useless. You should run no more than about 6psi of fuel pressure on a Holley-based carb. Get your fuel pressure right before you start tuning anything on the carb itself. Don't trust what the pump is supposed to be providing. Invest in a pressure regulator. We had a 6-9 PSI Carter that was delivering 14 PSI. That's more than enough pressure to blow the needles right off the seats.

[rubbinsracin]

we bought our carb from a guy that took it right off his 604 and put it on our steelhead motor. he said a starting point for his 604 was in cool weather 73s in front and 74 or 5s rear. then when it warmed up he would go to 75s front and 76s rear. i just think every motor is different. need to run it and check the plugs and go from there. your elevation, temp, humidity, etc. all factor in to how much jetting you need in my opinion.

[Matt49]

we bought our carb from a guy that took it right off his 604 and put it on our steelhead motor. he said a starting point for his 604 was in cool weather 73s in front and 74 or 5s rear. then when it warmed up he would go to 75s front and 76s rear. i just think every motor is different. need to run it and check the plugs and go from there. your elevation, temp, humidity, etc. all factor in to how much jetting you need in my opinion.

Hmm...going up on jet size for warmer weather sort of goes against common theory but whatever works I guess.
The problem described by racer10x sounds more like too much fuel pressure, bowls too high, or a blown power valve.

Racer10x,
What did the plugs look like?
If it's running really rich based on your plug readings, check the following:
Fuel pressure - no more than 6 PSI
Blown power valve - with the motor running, turn your idle mixture screws all the way in; if it DOESN'T kill the motor, your power valve is blown
If fuel pressure is okay and the power valve is okay, make sure your bowl settings are right.

[RacerX10]

Thanks guys, Ill check all that out and report back.

[llbullington]

We had the same problem. Dropped float level a little and stopped the problem off the corner. We also run 6psi.

[RacerX10]

We had the same problem. Dropped float level a little and stopped the problem off the corner. We also run 6psi.

what jets do you run ?

[RacerX10]

I'm about to give up on getting this Race Demon 750 to work on the 604, so I'm trolling for suggestions on a new carb.

I suspect any of the crate-specific carbs are going to be within a couple HP of each other, so "support" would be a deciding factor .. who's easy to get in touch with when you have problems ?

It looks like "stealth" and "willys" are popular choices, anybody have comments on either of those ?

Thanks.

[Egoracing]

Unless you are on 1/2 mile and larger tracks all the time a 650 would be my choice.

[RacerX10]

Will probably never be on anything larger than 3/8, and 90% of the time on 1/4's

It seems like I've read that a bone stock holly works fine on these motors, but I can't seem to find where I read that.

[50j]

I would call and talk to JDR, Willy's, and Stealth. Getting input from builders that do a lot of them might be a good idea.

[RacerX10]

I called Willy's this afternoon. Guy on the phone there was very helpful, and I liked that he was easy to get in touch with.

Shopping for a Willy's 604 carb now.

[jrkracing54]

I run a quickfuel crate carb. I have had no problems with it and the price tag was much less than Willy's, Stealth, K-B or Braswell. By hundreds! I am not on a deal or pushing them for any other reason than what I already stated. Just thought you may want to try to save a little $$$$$$$$$$. John 1*