914World.com [Powered by Invision Power Board]

Posted by: tsvo Nov 29 2016, 07:22 AM

I am looking fsome help. I have a 1973 1.7L. I have replaced the points and wires as well as general tune up. It starts fine and seems to idle OK. However after 30 - 45 Min of running it starts to bog down. The car loses power, idle drops then backfires. The car gets a quick power surge at the time of backfiring. THe cycle then repeats. I let the car cool down for a little while and it usually goes away.

Any sugestions?

Posted by: 76-914 Nov 29 2016, 10:12 AM

Did you replace the condenser also. Have you checked the coil's resistance?

Posted by: BeatNavy Nov 29 2016, 10:54 AM

Fuel injection or carbs? Initial thought is you're running way too rich or your timing is over-advanced. If FI, there are a couple of potential causes including blown MPS, fuel pressure too high, wonky CHT, etc. When you replaced the points, did you set dwell and timing? You need to adjust timing after changing or adjusting points...

If it is FI you may want to start getting familiar with this site: http://members.rennlist.com/pbanders/djetparts.htm

Posted by: tsvo Nov 29 2016, 12:38 PM

QUOTE(BeatNavy @ Nov 29 2016, 10:54 AM)

Fuel injection or carbs? Initial thought is you're running way too rich or your timing is over-advanced. If FI, there are a couple of potential causes including blown MPS, fuel pressure too high, wonky CHT, etc. When you replaced the points, did you set dwell and timing? You need to adjust timing after changing or adjusting points...

If it is FI you may want to start getting familiar with this site: http://members.rennlist.com/pbanders/djetparts.htm

Thanks, it is an FI. I did set the timing, but perhaps I need to recheck it. Any other thoughts are appreciated.

Posted by: tsvo Nov 29 2016, 12:39 PM

QUOTE(76-914 @ Nov 29 2016, 10:12 AM)

Did you replace the condenser also. Have you checked the coil's resistance?

I did not do the condenser. I will check that as well.

Posted by: rmital Nov 29 2016, 01:17 PM

QUOTE(BeatNavy @ Nov 29 2016, 11:54 AM)

.... If FI, there are a couple of potential causes including blown MPS, fuel pressure too high, wonky CHT,

solid advise...over the last 10 years of 914ing, the above was a good start and most of the time, the cause(s).
money's on the MPS of course, the most expensive solution

Posted by: Perry Kiehl Nov 29 2016, 05:28 PM

Check the MPS, CHT, and the distributor.

I worked on a car that had a similar problem, when it got hot the advance plate in the distributor wouldn't move freely.

Posted by: BeatNavy Nov 29 2016, 06:40 PM

QUOTE(Perry Kiehl @ Nov 29 2016, 06:28 PM)

I worked on a car that had a similar problem, when it got hot the advance plate in the distributor wouldn't move freely.

Good point, Perry. A good dizzy cleaning is also a worthy idea. The old grease gets sticky and dirty over the years. Relevant thread: http://www.914world.com/bbs2/index.php?showtopic=232335&st=0. Dizzy cleaning starts around post #36.

Rich would approve.

Posted by: tsvo Nov 30 2016, 06:47 AM

QUOTE(rmital @ Nov 29 2016, 01:17 PM)

QUOTE(BeatNavy @ Nov 29 2016, 11:54 AM)

.... If FI, there are a couple of potential causes including blown MPS, fuel pressure too high, wonky CHT,

solid advise...over the last 10 years of 914ing, the above was a good start and most of the time, the cause(s).
money's on the MPS of course, the most expensive solution

THank you, I will give it a try

Posted by: BeatNavy Nov 30 2016, 06:58 AM

Be methodical and follow the directions on that link I gave you for identifying the possible causes and eliminating them one by one through testing. You can do it, and you'll learn a lot about how to maintain it going forward. D-Jet is a pretty cool system, given its age, but if it hasn't been maintained something, or some things, will go wrong. If you have questions, let us know. Lots of good FI knowledge here on the World.

Posted by: Ansbacher Nov 30 2016, 11:23 AM

Had similar problem and turned out to be bad coil. Try a known good coil. Even if your existing coil checks out good cold, it might be bad when hot. I wasted a lot of time and money before I zeroed in on the coil. Good luck.

Ansbacher

Posted by: tsvo Nov 30 2016, 02:08 PM

QUOTE(Perry Kiehl @ Nov 29 2016, 05:28 PM)

Check the MPS, CHT, and the distributor.

I worked on a car that had a similar problem, when it got hot the advance plate in the distributor wouldn't move freely.

Thank you

Posted by: tsvo Nov 30 2016, 02:09 PM

QUOTE(Ansbacher @ Nov 30 2016, 11:23 AM)

Had similar problem and turned out to be bad coil. Try a known good coil. Even if your existing coil checks out good cold, it might be bad when hot. I wasted a lot of time and money before I zeroed in on the coil. Good luck.

Ansbacher

Thank you, I will give it a try.

Posted by: tsvo Nov 30 2016, 02:10 PM

QUOTE(BeatNavy @ Nov 30 2016, 06:58 AM)