Max

I have had a lot of success tuning my new 670 Street Avenger with the help of an Auto meter Air / Fuel ratio meter but I still get a hesitation when I punch it from a stop at idle to wide open throttle.

I have changed secondary springs but that didn't make any difference. I went back to the lightest spring in the kit because that doesn't seem to be the problem.

I think that what it really needed was an earlier/larger pump shot. I tried the more aggressive pump cams with some success. Now I have the brown pump cam on there which has a very radical lift and it seems to have helped the problem.

But now it compresses the spring on the lever. This causes the need for greater throttle pedal effort which I don't like. Is this compression of the spring going to cause any problems?

Should I maybee go back to the pink pump cam which does not have nearly the lift of the brown one and then increase the nozzle size one or two steps?

What it needs is a really early pump shot. which cam position is better for this number one or number two?

Let me know what you guys think. Thanks.

Jester

YES the harder pedal pressure can cause problems! Thats probably the pump arm bending when it binds at the bottom.

Take off the brown cam, there is no way you can use that. Something else is wrong. Try the orange or black to start. hole#1 is for motors that idle under 1000-1500rpm..hole 2 is for higher idle cars....so stick to #1.

Check the pump arm lash first. Do this by standing over the motor with it off..and working the throttle by hand a little bit. Fuel should begin coming out of the squirters right when you just start to move the throttle. there should be NO delay. Adjust the screw on the end of the pump arm to take out the play if you need to.

Max

Thanks Jester,

I went back to the pink cam and adjusted the arm. It works very smoothly.

When I put it on I used hole number two. I may be wrobng but it seems to me that #2 causes the cam to roll farther forward and I would think this would mean an earlier pump shot, but you are the second person that has told me that the #1 position will start the pump shot sooner than the #2 position. I'll give that a try.

The stock squirters are .031 should I step up one or two sizes?
Would that provide more fuel a little earlier on?

It only hesitates for like an instant then returns to a moderately rich burn and roasts the tires.

If I can cover up that flat spot the thing will be totally dialed in.

Max

Anybody know if steping up one or two nozzle sizes might cure the hesitation?

b92z28

As Jester said earlier in this post, the pump shot begins as soon as you step on the throttle. Niether of the holes start it any earlier than the other. Any time you give it gas, at idle or part throttle etc, it moves the accelerator pump.

Max

I have it adjusted so that the pump shot starts as soon as the throttle begins to open. The problem is that the lift on the pink pump cam doesn't provide enough volume of fuel to fix the lean condition. I think that by going from .031 to .037 squiter size I will get a greater volume of fuel with the same amount of pump cam lift. Hopefully enough more to eliminate the breif hesitation.

Otherwise it runs great. I highly reccomend the air/fuel meter as a tuning tool. Especially for people like myself going from TBI to carb because the oxygen sensor is already in place and the gauge is fairly cheap and easy to install.

Max

I tried a larger shooter and it now has great throttle response.
I went fro .031 to .037 which is two steps up and together with the green pump cam in the number 2 position I can crack the throttle wide open from idle and it never goes lean. It just roasts the tires. I thought I would let you know incase anyone else is having a similar problem.

BigL350

This post is a big help. I am having the same hesitation problem with my 670SA. I'll be ordering an O2 sensor kit at the end of this week, so hopefully I will start tuning next week. What accelerator pump cam does the 670SA come with, and which one did you wind up using after swapping to the larger pump nozzle? I'll be going through the same process you just went through, tuning a 670SA with an aftermarket A/F guage, so if there's anything else you can tell me that you think would help, it would be appreciated.

Thanks

Max

I think the 670- came with an orange pump cam. I'm using the green one in the #2 position and that has worked well for me.

I had to change the shooter size because none of the cams gave me the fuel it needed soon enough. Now, the larger bore of the nozzle lets out a greater volume of fuel sooner. That fixed the hesitation I had.