Jvette73

If you look at my sig you'll see my setup. Its a 600 vac sec(list 1850) that I bought new about a year or so ago. Ive jetted up the primaries to 67. I also put in the kit that converts the secondary "plate" to a "block" and jetted up a few sizes there too. I put in a lighter secondary diaphram spring that opens up the 4 barrel sooner and it all has worked great. But I still have a slight stumble when launching and dumping throttle hard from a stop. Im thinking I might need to tinker with the accelerator pump and whatnot. Ive seen the 50cc pumps available. Would my setup handle a 50cc pump in the primary? Should I also tinker with different pump cams? I see the cam on there now has more than one hole for location. Is it possible for me to solve this slight stumble by changing the position of my pump cam? The carb works great over all except for this slight stumble off the line. Every other department has been checked such as timing which is set to 14 initial and 36 total all in by 2500 with an additional 6 of vacuum advance. Thanks in advance for your insight.

dman535

Make sure that the slighest movement of the throttle starts fuel flow from the accel pump. If there is any delay it will cause a bog.

You may want to raise your float levels a bit, if they are a tab bit low it can cause a stuble.

What do the plugs look like ? You may want to increase your jet size up a bit as a lean mixture will cause that type of reaction.

Jvette73

dman535, i doubt im too lean as I see a slight blackining of plugs over time as well as the carbon build up on the exhaust tips. I had the primaries up to 68 but that was too much. I dropped it to 67 and seems to be just right. ill check the squirt in the throttle bores and how soon it reacts to the throttle linkage and get back to you. Heading out there now.

Vetterodder

I agree with Derek. Accelerator pump adjustment is a likely suspect. Also make sure that the transfer slots aren't too exposed also. If the idle speed setting is adjusted high enough some of your pump travel can be already taken up and you won't get as big of a shot as you should. That would also cause the engine to idle on the main circuit, causing an over rich mixture at idle. If your engine responds to changes in the idle mixtures screws, this probably isn't the problem. I wouldn't think your engine would need more than a 30cc shot. The 50cc pumps are deeper so, if you do decide to try one, make sure that you have the extra clearance between the carb and manifold for one first.


[Modified by Vetterodder, 6:08 PM 5/17/2003]

Jvette73

Derek, I can moce the throttle linkage about 1/8" before I see any gas from squirter. Its a #25 squirter. How do I get it to respond sooner?

Vetterodder, the engine will respond to idle mixture screws when adjusted so I dont think in set to high in idle to actuate main circut during idle. The pump shot looks weak. I have a spacer in between the carb and intake that holds the linkage for the BTO TV kit. Its not too thick but it looks like I might be able to add a 50cc pump with some slight trimming of spacer and maybe the top of intake. Do you know what size pump came with this carb? You mention a 30cc pump. Would that be what is on there from the Holley factory? How many different size pumps are available for the primary?

stalker

J...you may want to try changing your squirter size. I believe 1850s come with a 25, try going one size up and down to see if that helps.

Jvette73

stalker, my current squirter is in fact a #25. Its a really weak lookin shot when you view it thru the top of carb. Furthermore, when I load up holding the brakes against the convertor for launch im probably at 1/4 throttle already. Probably not much pump shot left after that. When I release the brake and slam the gas pedal, I get a slight stumble before the car moves forward. Also if im sitting relaxed at idle then slam the pedal down, I get a small poof sort of backfire and hesitation before the power comes on. Its been this way since I had this carb. Just looking for a way to improve things. Need to work on my launch and 60' times. Gonna have some sticky tires on the next time out at track. Dont want no delay. Want it all on asap. Any suggestions?


[Modified by Jvette73, 9:00 PM 5/17/2003]

dman535

Check out the pic :


You want to adjust the length of the bolt with the spring around it to get a good prelooad on the accelerator pump. There should be zero gap between the head of the bolt and the accel pump arm. Watch the spring as you move the throttle through a full stroke. The spring might need a little bit of shimming, just add a few washers to the head side of the bolt before the spring goes on, sometime they don't have enough tension to fully acutate the pump.

Check your float levels. The the level is to low the carb will delay in pulling fuel through the main metering circuit. You should have fuel just barely running out the holes when you pull the sight plugs out.

Vetterodder

I think you've found the problem. Like Derek said, the pump should start squirting as soon as the throttles begin to open. Adjust the pump linkage until it does. An 1/8" of travel before the pumps starts might not sound like much but half of that would still be a noticeable problem.

BSeery

If you do go to a 50 CC squirter you may have to add a spacer under the carb. Some times the larger housing and lever will run into the intake manifold.

stalker

J...if you've checked and your accelerator pump linkage is adjusted properly. I'd play with the sqiurters and the pump cam. I sounds like a cam that extends your pump shot maybe what you're looking for. A smaller squirter will also extend your pump shot. Also, make sure your powervalve is in good shape. Happy hunting...

Jvette73

Solved the stumble. But since I did a couple of things at one time im not sure what helped. Probably both. First off the ported vacuum source for the dist was registering vacuum at idle(950rpm) when it should not. So the primary throttle blades were too far open. From previous advice I had gotten, I adjusted the secondary stop screw to open the secondary blades just enough to allow some more air in. This raised the idle speed which allowed me to back off the primary idle enough to cancel the ported vacuum signal at idle. Ive know about this condition for with this carb ever since ive had it but just now corrected it. Living with this condition prior, one of my counter measures was to limit the amount of pull on the dist vacuum break. I did this since it was getting this advance at idle. Now that ive cancled the vacuum signal at idle I undid that limit. So before at idle the vacuum advance was already in. But now, with no signal at idle, im sitting at 12 degrees BTDC. But as soon as I hit the throttle, I get an instant 15 degree advance from the now, unlimited dist vacuum. The car has much better throttle response now. Now I can dump the throttle from a idle dead stop, and she takes off without hesitation, stumble or pop. Spins wheels easier now too. I may still expierement with a larger squirter nozzle ans see if it can get even better. Also gonna get a new set of plugs and try this side gapping trick Ive heard of. Thanks for all the input.

:cheers: :D

Gordonm

:cool: Got the problem solved. Always nice to cruise in a properly tuned car

Jvette73

yeah man, definatly runnin better now. I can cruise at lower speeds while in 4th with vertor locked and no get that chugging effect. Hopefully the extra air comming in thru the secondary plates will help lean out the idle some. Ill have to get some new plugs and run em for a bit then check em for color.

Couple more questions though.
Whice way to turn the idle mixture screws? Is it in for richer and out for leaner?

Also, I see the different holes in the linkage so you can put the pump cam in different positions. Theres 2 holes numbered 1 and 2. Whats the general effect achieved by changing the position? Right now its set on 2

Vetterodder

By reducing the amount of primary throttle needed you've killed at least 2 birds with one stone :). Besides allowing it to idle on the idle circuit, you're no longer already using up some of your pump travel which had left less available when you needed it. Except for a few models, the idle mixture screws go in (clockwise) for leaner and out for richer. The base setting is 1 1/2 out but final adjustment for your particular application may be something different. When turning in to fully closed, be gentle as the seats can be damaged if turned too hard. The best method to adjust them is with a vacuum guage. Adust for the higest reading while keeping both sides as equal as you can. As you increase vacuum, you'll probably also increase idle speed so you'll need to readjust the speed screw to compensate.

As far as the pump cam, IMO, if you're no longer experiencing any problems. leave `em alone. There may a be slight benefit from adjustment but if, "it ain't broke, don't fix it" :)