Throttle lag

[BGB1996]

I'm new to racing and into my second year in vintage FF. I'm currently chasing a problem with throttle lag when coming out of sharp turns. I replaced wires, plugs, diaphragm, distributor( from points to electronic ), adjusted the valves and played with the timing. Can you even get a instant response from the kent 1600 when you stab the gas pedal ?

[kea]

At what RPM ?

[Albatross]

If this is a relatively recent problem, check all jetts to be clean and unobstructed. I would think that for your type of racing, you would want to be a little on the lean side.The answer to your question about instant response is: yes

[Neil_Roberts]

I recommend sending your carburetor to the pro FF engine builder of your choice for a rebuild and the various tweaks that are known to improve it for FF service. If that's not a problem or not an option, you might consider a throttle linkage that opens both butterflies at the same rate instead of a primary/secondary linkage.

[Dick R.]

I've used an "off the shelf from Pegasus" Ivey race prepared carb since about 1992 for autocross. Linkage is progressive. No lag above about 3 - 3.5K. I use fresh street premium gas. Slight lag at lower rpm . . . where I shouldn't be anyway unless it is a tiny parking lot with no grip.

Dick
CM 85

[GT184]

If the air/fuel ratio is too lean you will hear the carb "spitting back".
- Fuel pressure too low
- Sticking needle/seat
- Float level low
- Enrichment system plugged/misadjusted/in-op. Not flowing enough fuel.


Too rich and you'll get a lot of black smoke out of the tail pipe, and the engine will stumble along until it is cleared out.

- Fuel pressure too high
- Sticking needle/seat
- Float level high
- Enrichment system misadjusted. Flowing too much fuel.

Dan

[S Lathrop]

Float level may be the problem.

When I was running FF, I would increase the weight of the float so it would ride lower in the fuel. This reduces the amount of fuel in the fload chamber. Then get the float level correct. The float level must be spot on. I would do a float level check most weekends.

The fuel level in a FF card is very critical.

[Buc01]

Billy,

I have to say that I reccomend the "take the carb off and send it to Ivey, Quicksilver, etc...." I have spent a LOT of time chasing down the same issue that you have on FF and FC cars. Eventually gave up and sent the carb off, got it rebuilt and returned, and presto no more lag, engine starts and runs great at all rpm.

Aaron

[bob darcey]

"Can you even get a instant response from the kent 1600 when you stab the gas pedal ?"

If you're like a lot of us, you want to be able to fix your own problems. I recommend that you get a copy of Jake Lamont's "How To Build And Maintain Competitive (But Legal) FF 1600 Engines" (Keith should have them). Assuming that the carb is race prepped (e.g., has dump tubes installed) and is in relatively good condition, you might try this from Jake's book (pg. 78):

"Since the secondary idle adjustment is available only from the bottom of the carb, it must be set before the carb is installed on the engine. Turn the screw in until the throttle plate just begins to uncover the first of the fuel transfer holes. If the plate is too low, either from misadjustment or wear on the idle stops, the fuel flow will be cut off and a SEVERE off-idle stumble will result. This will be particularly noticeable when the driver "blips" the throttle for a downshift. If the secondary throttle plate is too high, it will require the primary idle adjustment to be set too low and the same symptoms can occur."

[Hawke]

"Can you even get a instant response from the kent 1600 when you stab the gas pedal ?"

If you're like a lot of us, you want to be able to fix your own problems. I recommend that you get a copy of Jake Lamont's "How To Build And Maintain Competitive (But Legal) FF 1600 Engines" (Keith should have them). Assuming that the carb is race prepped (e.g., has dump tubes installed) and is in relatively good condition, you might try this from Jake's book (pg. 78):

"Since the secondary idle adjustment is available only from the bottom of the carb, it must be set before the carb is installed on the engine. Turn the screw in until the throttle plate just begins to uncover the first of the fuel transfer holes. If the plate is too low, either from misadjustment or wear on the idle stops, the fuel flow will be cut off and a SEVERE off-idle stumble will result. This will be particularly noticeable when the driver "blips" the throttle for a downshift. If the secondary throttle plate is too high, it will require the primary idle adjustment to be set too low and the same symptoms can occur."

Vote for this solution as well. Have seen many cars with this problem, and nearly all had an issue with the secondary idle ciruit. It is imperative to have the throttle plate just open, so the intermediate idle ports are just opened. The secondary barrel favours cylinders 1 and 4, so if it is out of wack, you may only get proper running on cylinders 2 and 3. Remember, this is only one you can alter when you adjust the idle mixture screw. When you snap open the throttle, it takes some time to get those cylinders to work properly on the main jets.

Dont forget to check the size of the secondary idle jet. I think it should be a 50, and off the shelf carbs come with a 55. Dont quote me on that size, as I am doing this from memory, but I'm sure someone will chime in with a correcting comment.

[Rick Kirchner]

All important points about carb tuning BUT:

Keith's question was VERY germaine - a newbie vintage guy coming off a slow corner - could be the car just isn't in the power band. Try it at same wheel speed and one gear lower, might not have the problem........might need a lower gear in that corner regardless.

I seem to remember a Witzenhof method (on a pinto) of checking throttle transient response (jetting and idle mixture). Same carb - ought to work on a 1600 as well.

[gcoffin]

Chase the carb problem yourself at the risk of having a string of bad weekends or send it to a pro. Last weekend of the year I lent my spare pro built carb to a noobie who was having trouble and he wanted to buy it on the spot......I said if you have to have that one just have Jay send me a new one....done deal.