pop on overrun

This forum is for topics and questions specifically related to the Mk III/Mk II variants.

pop on overrun

Postby alpappy » Sun Jan 09, 2011 5:57 am

Hi my 66 sprite pops on overrrun( 3rd 4th gear) If I just touch the accelerator it stops. Where do I start to stop this?

Thanks
alan
alpappy
Pit Crew
 
Posts: 5
Joined: Sat Jan 08, 2011 3:21 am

Re: pop on overrun

Postby trevor » Sun Jan 09, 2011 9:29 am

"pops" as back fire, or "burbling" pops? I've always had a bit of burble, but it is worse when the car is running rich or the timing is off.

My suggestion: If your car is in tune and it is not a back fire, then learn to enjoy the sound.
User avatar
trevor
1275cc
 
Posts: 796
Joined: Sun May 30, 2004 2:09 pm

Re: pop on overrun

Postby Jim Gruber » Sun Jan 09, 2011 2:02 pm

Trevor, could this be a case of the proverbial "Gulp Valve" needing to be replaced. Gulp Valve also known as a PCV Valve. I can recall on my HS Buddy's the new '68 Sprite having the PCV valve get plugged up and the thing backfiring every time he let off of the gas. Same type of sound.
Jim Gruber
Dayton, OH
Bugsy - 68 Sprite
Bugeye in Disguise
User avatar
Jim Gruber
1098cc
 
Posts: 295
Joined: Wed Jan 25, 2006 12:36 pm

Re: pop on overrun

Postby alpappy » Mon Jan 10, 2011 12:53 am

Thanks but this is British car and does not appear to have this valve fitted. Does changing the plugs with hotter or cloder ones make any diff
alan
alpappy
Pit Crew
 
Posts: 5
Joined: Sat Jan 08, 2011 3:21 am

Re: pop on overrun

Postby Bill Masquelier » Mon Jan 10, 2011 9:02 pm

Changing the plugs probably won't fix it-
If you have a 1275 in there then the gulp valve is often the cause (as Trev said). The gulp valve is not the PCV valve, the PCV valve creates a slight vacuum in the crankcase to prevent oil leaking out of the engine (among other things) while the gulp valve is supposed to dump extra air into the intake manifold when you take your foot off of the gas peddle to prevent exactly the problem that you are having (prevents the carbs from dumping a "rich" idle mixture when the revs are high which them "pops" in the exhaust pipe).
If your system is not up to specs them this will happen.
--On the other hand--- when I took the gulp valve and all of the other smog stuff off of my 1275 (but left the PCV valve in system to prevent oil leaks) the popping stopped completely! So much for theory vs. reality!
BillM
69 Sprite MkIV
Bill Masquelier
1098cc
 
Posts: 304
Joined: Tue Sep 07, 2004 2:53 pm
Location: Renton, Wa.

Re: pop on overrun

Postby alpappy » Tue Jan 11, 2011 12:54 am

HI It is the 1098 engine Does this have a gulp vlave or equivalent?
thanks
alan
alpappy
Pit Crew
 
Posts: 5
Joined: Sat Jan 08, 2011 3:21 am

Re: pop on overrun

Postby Charlie Tolman » Tue Jan 11, 2011 1:22 am

Pops or exhaust backfire, noticed during engine braking (overrun), is most likely caused by a lean air-fuel mixture.

High school days with a Ford flathead V-8 and dual exhausts: Backfiring was the "cool" event of any day, and the engine was tuned accordingly. Some would disconnect the engine vacuum hose (affected the timing, too ??), but the absolute best method to produce significant backfiring was to adjust the idle mixture jets on the carburetor. The air-bleed idle jets (tapered screws) were turned in, clockwise, until the engine would almost stall while idling, due to a lean idle mixture. Result: significant backfiring on overrun !!!

Possible causes on your Sprite:

* Air leaking into the intake and/or exhaust manifolds. Squirt starting fluid or WD-40 around gaskets, and notice if the engine idle speed increases. Be careful with highly inflammable starter fluid.
* Air leaking past the throttle shaft, due to excess clearance with the hole in the carb body. Use above technique to check.
* Too much spark advance.
* Lean air/fuel mixture at idle: Adjust the carb idle mixture screws; see a shop manual for the technique.

Here is a link to a problem and solution for a Sprite owner: (Note the British-cars.org part of the address).

http://webcache.googleusercontent.com/s ... re&ct=clnk

Charlie Tolman
Charlie Tolman
Judson Supercharged
 
Posts: 1199
Joined: Wed Mar 01, 2006 10:36 am
Location: Minnesota

Re: pop on overrun

Postby Bill Masquelier » Tue Jan 11, 2011 7:21 pm

1100 doesn't have a gulp valve- look into Charlie's input, rich it up some.
Bill
69 Sprite MkIV
Bill Masquelier
1098cc
 
Posts: 304
Joined: Tue Sep 07, 2004 2:53 pm
Location: Renton, Wa.


Return to MK III Sprite (MK II Midget)

Who is online

Users browsing this forum: No registered users and 1 guest

cron