Viva 1300GLS tuning help

[jgwilliamson]

Hi gang,

My 1977 Viva 1300 GLS is now back on the road after it's winter hibernation, but I'm having a bit of difficulty getting her to run smoothly. The problem is that the engine is responsive enough in in 1st and 2nd, but accelerating in 3rd and 4th at around 3000 (or about 50 mph) revs it starts to run inhibited, almost as though the choke has been pulled out. You then have to take your foot off the gas momentarily and then gradually re-apply to get the car to get past this. (It's a Stromberg CD 150 carb by the way).

I have checked out the following:

1. Replaced air filter.

2. Checked mixture with Gunson's Colortune. Got all the right colours for each of the 3 tests.

3. Cleaned spark plugs and checked gaps (Plugs looked in good shape..right colour on deposits on electrodes).

4. Fitted new contacts and condensor on dizzy (Bosch).

5. Checked timing with strobe.

The car idles nicely and everything seems fine, until as I say it gets to around 3000-3500 revs.

I'm sort of out of ideas of what to check next (fuel pump perhaps?). Can anyone suggest some other things to check/try ?

Thanks in advance

John

[mazzo]

Hi

Try the following if you haven't already.

Fill the damper pot on top of the carb with oil.

if that makes no difference, check the diaphragm in the carb. Look for any holes.

If they don't work, you could try the fuel pump or the coil. From your description, the responsiveness in low gears and then the lack of response in 3rd and 4th make me think of the carb though.

Good luck

[jgwilliamson]

Hi

Try the following if you haven't already.

Fill the damper pot on top of the carb with oil.

if that makes no difference, check the diaphragm in the carb. Look for any holes.

If they don't work, you could try the fuel pump or the coil. From your description, the responsiveness in low gears and then the lack of response in 3rd and 4th make me think of the carb though.

Good luck

Cheers Mazzo,

Done all the above , including a new diaprham - no joy.

I'm going to re-check points dwell and timing again just in case.

By the way.... I set the timing via strobe on #1 to 9 degree BTDC...I *thought* this was correct but now I'm not sure ...

Anybody confirm this?

Cheers

John

[mazzo]

Yes, 9 deg BTDC is right - for number 1 plug.

I always set it manually - not as spot on I guess as strobe but does the job. As long as you don't go past 9 deg and turn the crank anti-clockwise to get back to it, it works fine. Loosen the distributor bolt and take lead one off the plug. Rotate the distrib clockwise (past the point of spark) and then turn back slowly until it sparks.

How about the vacuum advance? Is it working. Take off the hose and check for any splits. I have the older delco distributor, but used to check it by sucking on the pipe and seeing if the plate moved.

Someone else might give better advice with the bosch distributor as I have next to no experience with it (apart from on a chevette some years ago).

Best of luck.

[lambaj]

Sounds like fuel starvation to me. 1st and 2nd gear are over very quickly, and will not give the engine enough time to empty the carb fuel bowl, 3rd and fourth involve longer throttle times and if you have insufficient fuel flow, or pressure then you will start to run out. More revs and time = more fuel requirments.

There are a few possibilities:

1) Fuel pump diaphram perforated (be careful, a leaky diaphram can fill the sump up with fuel..... BOOM!)

2) The fuel pump could be blocked with crud out of the tank

3) The float chamber needle valve could be stuck, or the float level wrong.

4) As happened to me, a bit of rubber came off the fuel hose and sat on the inlet to the float chamber valve - took me for ever to locate. Worth a check.

5) the fuel tank could be full of rust/crud and blocking the feed pipe.

6) the fuel hose to the pump could have been crimped by a jack, or some bit of rubbish kicked up off the road.

Lots of stuff to check, but hopefully one will be the culprit


7, silly one - is the air filter blocked ?(would have to be REALLY bad!)

Good luck
Tony (HA21)

[jgwilliamson]

Yes, 9 deg BTDC is right - for number 1 plug.

I always set it manually - not as spot on I guess as strobe but does the job. As long as you don't go past 9 deg and turn the crank anti-clockwise to get back to it, it works fine. Loosen the distributor bolt and take lead one off the plug. Rotate the distrib clockwise (past the point of spark) and then turn back slowly until it sparks.

How about the vacuum advance? Is it working. Take off the hose and check for any splits. I have the older delco distributor, but used to check it by sucking on the pipe and seeing if the plate moved.

Someone else might give better advice with the bosch distributor as I have next to no experience with it (apart from on a chevette some years ago).

Best of luck.

Cheers Mazzo,

Vacuum advance seems fine.

I'm setting the various ignition bits using a Gunsons strobe and also a Gunson's Sparktune test meter.

The funny thing with the latter is that when you use it to set the correct dwell (48-52 degrees according to their sheet), the resultant points gap is about 0.017 " , which seems a lot different from the Delco setting of 0.022" for new contacts.

Anybody got a Chevette manual to check the Bosch settings ?

Cheers

John

[jgwilliamson]

Sounds like fuel starvation to me. 1st and 2nd gear are over very quickly, and will not give the engine enough time to empty the carb fuel bowl, 3rd and fourth involve longer throttle times and if you have insufficient fuel flow, or pressure then you will start to run out. More revs and time = more fuel requirments.

There are a few possibilities:

1) Fuel pump diaphram perforated (be careful, a leaky diaphram can fill the sump up with fuel..... BOOM!)

2) The fuel pump could be blocked with crud out of the tank

3) The float chamber needle valve could be stuck, or the float level wrong.

4) As happened to me, a bit of rubber came off the fuel hose and sat on the inlet to the float chamber valve - took me for ever to locate. Worth a check.

5) the fuel tank could be full of rust/crud and blocking the feed pipe.

6) the fuel hose to the pump could have been crimped by a jack, or some bit of rubbish kicked up off the road.

Lots of stuff to check, but hopefully one will be the culprit


7, silly one - is the air filter blocked ?(would have to be REALLY bad!)

Good luck
Tony (HA21)

Cheers Tony,

I'm beginning to think the problem may indeed lie with fuel problems. I've been through the electrical side a couple of times now and just in the last hours replaced the distributor cap and rotor arm - no change.

The fuel line has a filter fitted just before the pump so hopefully nothing untoward has got stuck in the pump (or beyond!).

I'll check out the fuel line from tank to carb to check all well...I may even have a spare fuel pump in the garage somewhere (bit of a job locating it though )

I'll let you know how I get on

Many thanks

John

[jgwilliamson]

A quick update on where I'm at with my tuning problems.

Thanks to previous advice I came to the conclusion that it was the carburation that was the problem, so I phoned the folks at "Carburetter Exchange" (see http://www.carbex.demon.co.uk ) for some help and advice, and also prices on refubishing the CD150.

During the conversation the chap at C.E. said that as the units get older and the needle and jets start to wear the carb tend to burn rich when at idle. Most people (including MOT testers) will then turn down the mixture, which is OK at low revs, but leads to fuel starvation at higher revs (!!)

This rang a bell as the MOT tester a couple of weeks ago mentioned that he had had a problem getting it through the emissions test and presumably turned down the mixture.

Anyway I played around with the mixture and the problem has more or less disappeared. It still needs some proper final adjustment with the colortune, but at least it is now driveable whereas it wasn't before.

I'm a bit annoyed with myself as checking with the colortune was the first thing I did, and from the results it "looked" like it was OK so I took that for granted. Just goes to show that you shouldn't trust these "gizmos" implicitely!

At least I can now happily get to some shows this summer, and will send the carb to C.E. at the end of the season for a re-furb.

Many thanks for all the help and advice.

John