1.7 B172K rpm varies, running uneven.

Post by **webracer** » 10 Jul 2006 06:37 pm

My volvo 340 gl 1.7 is running unstable.

I took the carburetor apart, replaced gaskets. That did not help.
Don't think it is an air leak problem.

The rpm vary from 900 to 1200.... they are however quite stable for a few seconds...

The car is not good to drive on idle either.....for instance driving down a hill without using the gas pedal, the speed varies slightly.

If i put the car in neutral and push the gas pedal so the engine runs at for instance 2500rpm the engine is also then running slightly uneven...not being able to hold exactly 2500rpm

I opened the accelerator pump in the carburetor, and there were two tiny holes in the gasket. Not big though.
Is there a lot of air/fuel pressure here? Can this be what is causing it? If not, what other things should I check?

Any ideas?

Thanks,
Trond

Post by MJ » 10 Jul 2006 06:45 pm

As to the bad driving on idle, I think they're all like that. If I cruise along with no gas, when the car slows to a certain speed, it will get very jerky and clutch must be pressed in. Don't worry about that.

As for the bad running is there a loss of power under heavy acceleration, or is just a bit rough? Have you checked the distributor, these tend to wear out quickly...

Post by **webracer** » 10 Jul 2006 07:19 pm

The car acceleration is good... No loss of power. I've noticed however, if I push the gas pedal fully, wait a second or so, take my foot of the pedal, and then instantly push it fully again. Then the car might stutter a bit before accelerating again. I guess this is normal?

The distributor was changed recently. Don't know about the spark plugs though.

The uneven rpm problem appeared after I ran the car at high speeds. The engine did not overheat or anything, but it was running unstable since that.

About the accelerator pump...
If i push the accelerator pump on the carburetor, there is a tiny bit gasoline comming out of the pump.

The engine has run 215000km, how long does the engine last?

Post by **SteveP** » 10 Jul 2006 07:33 pm

Might be way off... but the 1.7s are notorious for carb base warping that could've been missed even by taking the carb apart. Although you say you think it's not an air leak... even so, it's a common fault that I thought I'd add

Post by **pettaw** » 10 Jul 2006 07:41 pm

yeah, sounds like classic 1.7 air leak from the carb/inlet manifold to me. time to find a new carb.

Post by **webracer** » 10 Jul 2006 08:04 pm

Thanks for all replies!

I replaced the two big plastic "gaskets" at the bottom of the carb. And the thin gasket that goes under these to also.
I was sure there were no air leaks, but go figure.

I sprayed around the bottom of the carb with startergas. The rpm incereases noticebly. I do not understand where the air leak is, because I have just replaced all the gaskets at the bottom of the carb!

I tightened all the screws too... and the gaskets at the top of the carb look good.

Would a new carb really help in this situation? is the carb itself bent/broken so the gaskets won't seal?

What do you mean by warping?

Post by **pettaw** » 10 Jul 2006 08:50 pm

yup, exactly, the carb base bends so it doesn't seal properly.

Sometimes the flange on the inlet manifold where the carb attaches to also bends upwards as well.

Post by **webracer** » 11 Jul 2006 05:30 pm

I removed the carb again, and the base was bent. One millimeter at least.
So I used 240 grain sandpaper (finished with 400) and after a while I got the carb base pretty even

Also used gasket cement directly on the manifold to ensure no leakage there.

That helped! The car runs smooth now.

I've noticed another problem though. When I drive slow, idle.....on a level road, sometimes it seems the wheels are not in contact with the engine.
Just one half a second or so. So the car goes back and forth.
Is there bearings or something that may need tightening?

Post by **jtbo** » 13 Jul 2006 02:41 pm

webracer wrote:I removed the carb again, and the base was bent. One millimeter at least.
So I used 240 grain sandpaper (finished with 400) and after a while I got the carb base pretty even
Also used gasket cement directly on the manifold to ensure no leakage there.

That helped! The car runs smooth now.

I've noticed another problem though. When I drive slow, idle.....on a level road, sometimes it seems the wheels are not in contact with the engine.
Just one half a second or so. So the car goes back and forth.
Is there bearings or something that may need tightening?

That last problem is quite annoying, I think with fresh engine and gearbox mounts it does not feel so bad, but basicly it is that engine does not burn fuel properly, I'm still getting bit of it even I have replaced ignition and carb with completely different systems and only solution to that is run overrich mixture, is bit odd why it acts like that, but that is way it likes to work for me at least

Website · Post by **antiekeradio** » 13 Jul 2006 05:11 pm

sandpaper has saved me a few of those carbs too...

best way to flatten the base is to put a new sheet of sandpaper (grain 240?) on a piece of window glass, preferably the thickest type you can find laying around. doesn't need to be large.

The carb should be pressed down lightly and slid across the sandpaper in a 'rotating eight' pattern. this way it sands off evenly and flat.

you will notice the edges will become sanded first, and the center parts only much much later.

the bolts of the carb should be done really lightly. there are spring washers in between too, these should NOT be pushed flat all the way!

Post by **pettaw** » 13 Jul 2006 05:56 pm

Spec of bolts is 14Nm, which is moderate. Don't hang off the spanner on these

I had to do exactly the same to the inlet manifold, although I just used a very large file being extremely careful to hold it flat.

Also a good tip is to stuff a greasy rag into the hole of the manifold so that your engine doesn't inhale the filings when it starts up