vaccum caps..thank you and ?

[22lyons]

So i just checked the vaccum caps on carbs as advised due to backfire on decel. Just as was mentioned they were both cracked badly so i replaced.

 

Will there be any performance differences since the leak is fixed? Will it impact mpg? I guess other than the backfire on decel what other issues does the leak effect?

 

Thanks for all the good info! What a great site.

 

Larry

[V7Goose]

There generally will not be any other detectible changes. The vacuum leak from old caps is very slight - not even enough to noticeably affect idle. But it IS enough to upset the total fuel burn enough to cause the afterburn on decel. That is because the engine is already set up to run on the ragged edge of too lean to start with (as all new engines are).

Goose

[22lyons]

My idle was not staying constant...maybe this could help.

 

Thanks so much.

 

  V7Goose said:

There generally will not be any other detectible changes. The vacuum leak from old caps is very slight - not even enough to noticeably affect idle. But it IS enough to upset the total fuel burn enough to cause the afterburn on decel. That is because the engine is already set up to run on the ragged edge of too lean to start with (as all new engines are).

Goose

[V7Goose]

  22lyons said:

My idle was not staying constant...maybe this could help.

 

Thanks so much.

What do you mean by "not staying constant"? If it was surging, that indicates a too-rich condition, probably caused by the choke partially on or one of the plungers hung up.

 

The vacuum leak from the caps is generally only significant when the throttle is chopped at high RPM (like shifting or deceleration), which creates a very high vacuum state in the intake, enough to cause the minor leak to get significant.

Goose

[22lyons]

the idle will slow a bit then pick back up to normal. so it is not a surge just a very slight slow for a split of a second and then back to normal.

 

  V7Goose said:

What do you mean by "not staying constant"? If it was surging, that indicates a too-rich condition, probably caused by the choke partially on or one of the plungers hung up.

 

The vacuum leak from the caps is generally only significant when the throttle is chopped at high RPM (like shifting or deceleration), which creates a very high vacuum state in the intake, enough to cause the minor leak to get significant.

Goose

[Sailor]

While we are on the topic. I just put on a set of LA Chopper slipons. Now on deceleration I get multiple backfires. This is not good. Where I live there a lot of hills. I find that if I keep just a tiny bit of throttle on while coasting down the hill I do not get the backfiring. I have checked the caps and they are fine. It was not backfiring before.

Suggestions?

[V7Goose]

  Sailor said:

While we are on the topic. I just put on a set of LA Chopper slipons. Now on deceleration I get multiple backfires. This is not good. Where I live there a lot of hills. I find that if I keep just a tiny bit of throttle on while coasting down the hill I do not get the backfiring. I have checked the caps and they are fine. It was not backfiring before.

Suggestions?

Exhaust leak where the new mufflers clamp or the mufflers are just too short and open.

Goose

[Sailor]

Thanks.