Swapped resonator/downpipes: now idle unsteady (72 250 w114)?

[Jub]

I had resonator and downpipes replaced at muffler shop. Drove in humming, now limping back (feels like low/unsteady idle; carbs)? 72 250!w114.

Any one ever experienced this?

Jub

[kraakevik]

My '73 114 280 with a DOHC six had three-to-one headers and dual pipes back to the resonator. If the replacement pipes and resonator materially affected the breathing and back-pressure the carburetors may need to be adjusted or even re-jetted--good luck





Tim Kraakevik
kraakevik@voyager.net
630 940-2420

[dobrodan]

It sounds like a vacuum leak, which could have been caused whent they changed the downpipe.

[Jub]

Kraakevik/Dobrodan thanks, you guys may be on to something.

The two pipes originally going into the resonator was fitted with a Y pipe to make it go into the new resonator (which was a single pipe fitting). Also, old resonator had major leak in exhaust, which I kind of let be because I never really trusted that resonator (was always worried it was clogged: ~50 years old)...so possible breathing majorly affected. Saw talk on motorcycle forums that when pipes are modified you have to always reset/rejet carbs. Just strange that on this forum, few have ever encountered this... So kind of leaning towards vac leak caused by swapping down pipes.

Leak at downpipes, any quick method to check and where exactly (where down pipes bolt on or further down or up)? I’ve used carb cleaner in past to detect poorly seated carbs, is this the way to detect poorly seated downpipes as well?

Thanks again,

Jub

[kraakevik]

The early USA cars had EGR piping that fed into the exhaust pipes downstream. If the EGR connection is still open to atmosphere that won't help, but it's probably been clogged for years.

It's conceivable that vacuum tubing may have been dislodged when the new exhaust was installed--you might check to see if you have low vacuum and try to find any loose ends.

The reduced flow at the Y-pipe may in fact necessitate re-jetting--best of luck



Tim Kraakevik

[Jub]

Found issue, but now have another issue.

So looks like when muffler guy swapped downpipes, he snapped fuel cutoff wire leading to one of Weber carbs. There is a 12 volt wire that (when ignition is switched on, opens primary jets and allows fuel into carbs). Reconnected, then went to start car and nothing happened?

Charged battery, tried again next day...nothing (car doesn't even crank). Went to autozone to r/o battery, they tested and was fine. Starter is ~2 years old, so started to look there. Was able to get 12 volts directly to lower bolt on solenoid and heard starter motor run (so looks good as well). Keep in mind downpipes bolts are right next to starter, so still possible they screwed this up?

Lastly, was able to turn engine clockwise, so engine isn’t seized. Thinking might be ignition switch, or relay or...thoughts?

Jub

[kraakevik]

Too many coincidences to my mind for the failure to be unrelated to the muffler work.

Did they dislodge or sever the woven copper grounding strap from the starter?

I'd suggest jumpering the grounding strap to see whether the starter comes back to life. Sometimes the woven strap looks fine but builds up corrosion internally--best of luck


Tim Kraakevik
kraakevik@voyager.net
630 940-2420

[Jub]

Copper ground was touched, but looks intact for the most part (frayed on one side but looks 95% intact).

Jeez, this is why I do my own work and hate/fret when others muck with my cars. Muffler work/body work is really only time I hand over my keys...

Jub