Pagoda SL Group

W113 Pagoda SL Group => Drive train, fuel, suspension, steering & brakes => Topic started by: Ivory250SL on October 19, 2012, 13:12:21

Title: 250 SL hesitation and backfire into intake when hot
Post by: Ivory250SL on October 19, 2012, 13:12:21

Hello group. my `67 250SL hesitates and backfires into the intake when hot at low revs, after investigation on this forum i looked at the WRD, cleaned and lubricat it, no result.
When i loosen the lower bolts of the WRD with engine warm (180degrees F) the backfire and hesitation stops and it runs smooth, so i add some washers.
I thought wrong, problem is when i start it cold again it runs terrible.

When i make the rod at the fuelpump longer its gets better (gets more fuel)

Does anybody now how to rich the mixture?

Thanks.

Title: Re: 250 SL hesitation and backfire into intake when hot
Post by: w113dude on October 19, 2012, 21:22:03

backfiring is usually result of not enough fuel, I would look in to fuel system before doing anything else make sure fuel pump is delivering as it should flow and volume. do the test at the return line at the gas tank.

Title: Re: 250 SL hesitation and backfire into intake when hot
Post by: ctaylor738 on October 20, 2012, 22:19:42

I recommend that you put the WRD back the way it was originally.  Shims under the WRD are like a last resort for a problem like this.

The first thing to do is to make sure you are not getting too much air at hot idle. 

Disconnect the linkage to the pump.

Disconnect the linkage from the fitting on the throttle plate and move the plate by hand.  Make sure that when it is fully closed, you can feel it "stick" or "bind."  Adjust the stop as needed.  Remove the rubber boot at the front of the throttle body.  With the engine idling, put your hand or a piece of paper over the air intake and make sure that there is no suction.  Pinch the idle air hose with pliers - the engine should die.  If it doesn't you need to find the cause of the extra idle air. 

You should now be able to adjust the idle mixture with the thumbwheel on the back of the pump to get a good idle - use a CO meter or take the "linkage tour."

Then adjust the ends of the linkage rods to the position of the levers.

Title: Re: 250 SL hesitation and backfire into intake when hot
Post by: Neil Thompson on October 21, 2012, 12:07:56

I had a similar problem recently and got good advice off the forum, I would first check your ignition timing and then go to fuel.

Have a look at this thread which advice from stickandrudderman got to the route of the problem http://www.sl113.org/forums/index.php?topic=17098.msg118011#msg118011

Good luck

Title: Re: 250 SL hesitation and backfire into intake when hot
Post by: Ivory250SL on November 02, 2012, 18:58:44

thanks for the replys (sorry for the delay),
first i put eveything back as it shut be , than i checked for falls air like Chuck discript, all good there, and took the linkage tour, found out that i forgot to adjust the idle switch on the venturi
(i restored the car and everything has been apart), makes a hole lot of difference.
But not out of the woods yet; so i looked further, ignition; everything is new and on time, so i didnt look further on that.
Then i went to look at the fuel system as Shaun mentioned, i put the fuel pump of my brothers car on it (is brand new) no differnece, than after investigation i turned the full load screw on the IP 1/4 turn to the left, Yep...problem solved, just a very little bit of hesatation (think i give it another 1/4 turn), but it drives fine now.

thanks for thinking with me..

regards,

Armand.