250 crossflow flat spot - Page 2

Topsy11 · 02-12-2018, 07:07 PM

Quote:

Originally Posted by yearby

All you need to know is it holds vacuum and that it moves the points contact mechanism when vacuum is applied.

It does just that. If I suck on it the timing advances and idles up.

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Topsy11 · 02-12-2018, 07:26 PM

Quote:

Originally Posted by solarite_guy

Yes it will run like crap if running atdc. Under load can burn the exhaust valves too.

The very least amout of advance should be what is stated in the manual. Those settings were very conservative and matched with the low cr and retarded valve timing of the day made for lethargic engines. I am assuming you have a stock camshaft.

I know a lot of things are being presented. List them and try 1 thing at a time and cross things off the list.

Pretty much everything that has been listed are possibilities.

I have my own order of things to try, but I want to avoid the "too many cooks in the kitchen" scenario.

After you have gone through the list of tests here and if the problem persists, then I'll add my 2 cents if there is anything still to test.

Hang in there.

Make sure Peter has a chance to review your results vs tests.

So timing is correct with peter. The only things left are my pcv I'm waiting for because the hose just sits in the crank case and maybe a fine carby tune. Everything else here has been checked and is good.

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yearby · 02-12-2018, 07:33 PM

Quote:

Originally Posted by Topsy11

So after all that retiming. It's the same. So I'm guessing not timing after all. When I reply the vacuum advance on the dissy after setting timing the idle goes up and so does the timing to around 10 btdc. Besides that I'm guessing I may just put an electric dissy in and go from there.

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When you apply the vacuum hose onto the vacuum advance, it should increase the engine idle revs and the amount of advance, but I'm thinking that 10 degrees is a little too much. You maybe getting too much vacuum to the vacuum advance.

As a test, disconnect the vacuum advance and block it, then run the engine and see if it still has the flat spot, backfire?

Also, when you have the vacuum advance hose connected reset the engine idle speed to spec, it should be idling too high.

Unless there is something seriously wrong with your dissy, a electronic dissy will not solve the problem, but would be nice.

Topsy11 · 02-12-2018, 07:43 PM

Quote:

Originally Posted by yearby

When you apply the vacuum hose onto the vacuum advance, it should increase the engine idle revs and the amount of advance, but I'm thinking that 10 degrees is a little too much. You maybe getting too much vacuum to the vacuum advance.

As a test, disconnect the vacuum advance and block it, then run the engine and see if it still has the flat spot, backfire?

Also, when you have the vacuum advance hose connected reset the engine idle speed to spec, it should be idling too high.

Unless there is something seriously wrong with your dissy, a electronic dissy will not solve the problem, but would be nice.

That's tomorrows job. I have not tried blocking the vac advanced and throttling. I will lower.the idle and try again. Get back to u.with results

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yearby · 02-12-2018, 07:50 PM

When you reset your idle speed, also reset your idle fuel mixture, make sure the auto choke is not engaged.

Topsy11 · 02-12-2018, 07:54 PM

Quote:

Originally Posted by yearby

When you reset your idle speed, also reset your idle fuel mixture, make sure the auto choke is not engaged.

I'm not sure what the fuel idle mixture screws is. Or which way I'm turning. Carby is not my specialty. Am I turning a screw to lower.the fuel?

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yearby · 02-12-2018, 09:03 PM

There is a mixture screw at the base of the carburettor, this is the fuel mixture screw for idle.
On a pre emission carburettor you wind it out to add fuel.
On a emission carburetor you wind it out to add air to lean mixture.

On a emission carburetor the mixture screw may be hidden behind a plug to prevent tampering and which was to prevent people changing the vehicle emissions.

I don't know when the change is mixture screw setting came into effect, you will have to use your initiative here.

All I really want is you adjust until you have a nice steady idle at the specified rev's before we go on with the diagnoses.

When you fit the new PCV, you will need to reset this.

yearby · 02-12-2018, 09:05 PM

If the mixture screw does not have any effect on idle condition, you may have a vacuum leak?

Topsy11 · 02-12-2018, 09:07 PM

Quote:

Originally Posted by yearby

If the mixture screw does not have any effect on idle condition, you may have a vacuum leak?

Not a problem. When my pcv arrives this week I will adjust this instead of the idle screw. Will post my results. Thank you heaps

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Topsy11 · 02-12-2018, 09:13 PM

Quote:

Originally Posted by yearby

There is a mixture screw at the base of the carburettor, this is the fuel mixture screw for idle.
On a pre emission carburettor you wind it out to add fuel.
On a emission carburetor you wind it out to add air to lean mixture.

On a emission carburetor the mixture screw may be hidden behind a plug to prevent tampering and which was to prevent people changing the vehicle emissions.

I don't know when the change is mixture screw setting came into effect, you will have to use your initiative here.

All I really want is you adjust until you have a nice steady idle at the specified rev's before we go on with the diagnoses.

When you fit the new PCV, you will need to reset this.

Also it has a manual choke. So I'll turn the fuel screw to lower the revs. Sounds easy. I'll get back to u

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yearby · 02-12-2018, 09:18 PM

Quote:

Originally Posted by Topsy11

Also it has a manual choke. So I'll turn the fuel screw to lower the revs. Sounds easy. I'll get back to u

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There is a idle speed adjustment screw on the throttle linkage to adjust the idle speed. The mixture screw is to adjust idle quality to where it runs best.

Itsme · 02-12-2018, 09:24 PM

Quote:

Originally Posted by Topsy11

So timing is correct with peter. The only things left are my pcv I'm waiting for because the hose just sits in the crank case and maybe a fine carby tune. Everything else here has been checked and is good.

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Missing pvc valve could be your backfire problem as it will upset your engine vacuum, this can cause leaner fuel/air mixture ratio making it more volatile resulting in backfiring.

yearby · 02-12-2018, 09:35 PM

Quote:

Originally Posted by Topsy11

https://www.youtube.com/watch?v=V1fN...&feature=share

Here is some vids. Of the timing and the flat spot. I dont throttle.to hard or it goes bang or dies on its butt

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Watching your first video, it looks like it could be the carburettor accelerator pump not working, or partially blocked or not getting fuel.

My other thoughts where maybe burn valve or too much advance, but the above seems to be plausible at this moment.

When you have a problem no one can solve, you must go back to basics and check everything and eliminate possible causes until you solve it.

Topsy11 · 02-12-2018, 09:40 PM

Quote:

Originally Posted by yearby

Watching your first video, it looks like it could be the carburettor accelerator pump not working, or partially blocked or not getting fuel.

My other thoughts where maybe burn valve or too much advance, but the above seems to be plausible at this moment.

When you have a problem no one can solve, you must go back to basics and check everything and eliminate possible causes until you solve it.

How do I check the accelerator pump. If it's not running and I press the pedal fuel squirts into the carby. So u think not enough fuel pumping I and.its to lean?

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yearby · 02-12-2018, 09:41 PM

Quote:

Originally Posted by Topsy11

https://www.youtube.com/watch?v=3smv...&feature=share

Here is some vids. Of the timing and the flat spot. I dont throttle.to hard or it goes bang or dies on its butt

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On your second video, the engine is running too fast for the idle speed.

Topsy11 · 02-12-2018, 09:43 PM

Quote:

Originally Posted by yearby

On your second video, the engine is running too fast for the idle speed.

It runs faster when I put the vacuum advance back on. I'll lower the idle using only.the fuel screw.

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yearby · 02-12-2018, 09:51 PM

Quote:

Originally Posted by Topsy11

How do I check the accelerator pump. If it's not running and I press the pedal fuel squirts into the carby.

Yes that is correct

So u think not enough fuel pumping I and.its to lean?

Maybe?

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It could be what Officemanager suggested.

"Missing pvc valve could be your backfire problem as it will upset your engine vacuum, this can cause leaner fuel/air mixture ratio making it more volatile resulting in backfiring."

Completely block off your PVC and try running the engine again and see if it reduces the back fire.

Topsy11 · 02-12-2018, 09:52 PM

Quote:

Originally Posted by yearby

It could be what Officemanager suggested.

"Missing pvc valve could be your backfire problem as it will upset your engine vacuum, this can cause leaner fuel/air mixture ratio making it more volatile resulting in backfiring."

Completely block off your PVC and try running the engine again and see if it reduces the back fire.

If I put my finger over the pcv hose it stalls. Should that not happen?

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yearby · 02-12-2018, 09:55 PM

Quote:

Originally Posted by Topsy11

It runs faster when I put the vacuum advance back on.

Yes that is correct.

I'll lower the idle using only.the fuel screw.

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No, lower the idle speed using the screw that is on the throttle shaft.

Set how well (smooth) the engine run with the mixture screw. (the one at the base of the carburettor).

Topsy11 · 02-12-2018, 09:57 PM

Quote:

Originally Posted by yearby

No, lower the idle speed using the screw that is on the throttle shaft.

Set how well (smooth) the engine run with the mixture screw. (the one at the base of the carburettor).

Check got it

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Topsy11 · 02-12-2018, 09:58 PM

Quote:

Originally Posted by yearby

It could be what Officemanager suggested.

"Missing pvc valve could be your backfire problem as it will upset your engine vacuum, this can cause leaner fuel/air mixture ratio making it more volatile resulting in backfiring."

Completely block off your PVC and try running the engine again and see if it reduces the back fire.

I will do it again to.orroe to be sure as it stalled when the retarded mechanic put his finger over it

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yearby · 02-12-2018, 10:05 PM

Quote:

Originally Posted by Topsy11

I will do it again to.orroe to be sure as it stalled when the retarded mechanic put his finger over it

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I think you have found your problem with the engine not having it's PCV.

It's getting too much air without it and too little air when it is plugged.

Do you have access to another vehicle with a PCV to steal and fit to your engine and do a test to eliminate the problem?

Topsy11 · 02-12-2018, 10:12 PM

Quote:

Originally Posted by yearby

I think you have found your problem with the engine not having it's PCV.

It's getting too much air without it and too little air when it is plugged.

Do you have access to another vehicle with a PCV to steal and fit to your engine and do a test to eliminate the problem?

I will.steal one off my xr8 or xr6 they look very similar.

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GCRXR6 · 03-12-2018, 02:19 AM

As Yearby said, you need that PCV. Gee, PCV's should be everywhere at the wreckers. A new one isn't necessary. Just find one, out of the same engine type and give it a good clean and rinse in solvent until it rattles freely. The things are virtually indestructible. Also, if you aren't sure about the accuracy of the idle mixture setting, a good starting point is to, screw it in all the way (gently), then back it out a turn and a half. That should get it very close. You may have to screw it in a little to lean it off until the idle is smooth.

Olbucko · 03-12-2018, 12:02 PM

The engine won't run properly without the PCV valve, as the previous post says, almost anything will do, (I use a PCV from an FGX in an XT 221 log head motor)
Also you can't time an engine accurately without a timing light because of wear and tear in the timing chain and distributor. The book says 6 degrees +or-2, see attached page from factory XD-XC WSM. I had a 250 crossflow for 15 years and it ran quite happily set at 10-12 Degrees BTDC
Check the condenser, if it's on the way out it can cause the motor to misfire or stall under load.

Topsy11 · 03-12-2018, 01:14 PM

Quote:

Originally Posted by Olbucko

The engine won't run properly without the PCV valve, as the previous post says, almost anything will do, (I use a PCV from an FGX in an XT 221 log head motor)
Also you can't time an engine accurately without a timing light because of wear and tear in the timing chain and distributor. The book says 6 degrees +or-2, see attached page from factory XD-XC WSM. I had a 250 crossflow for 15 years and it ran quite happily set at 10-12 Degrees BTDC
Check the condenser, if it's on the way out it can cause the motor to misfire or stall under load.

The xd xe motor although the same but newer do they use basically the same specs as a 1978 engine? I will retime with my pcv valve on (was 9bucks new) and adjust my idle and idle mixture and all that and see how much of a miss it may still have. One bloody piece of this purple ruins all.the other pieces I adjusted previously. If I advance mine to 10 ish even though the book says 4 it will only ping so.ill know to back it off.

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Topsy11 · 10-12-2018, 05:19 PM

Soooooo I put my.pcv valve on. Adjusted the idle and the idle curb. I adjusted the mix screw and turned it in 1.5 turns (to the right) and it started to idle up. Got it idling nice. Idles in drive and does not start to labour. Flat spot is still there. Not as bad but still there. If I punch it from idle it pops half the time and not the other half. If it's not idling it very slightly pops but revs up. My timing is suppost to be done at operating temp with the vacuum advanced hose off. In drive or neutral? The timing is sitting at 10degress after adjusting my idles and screws in neutral. When the vacuum advanced is off it sits at 4 ish. Sp making progress. Better with pcv valve and adjusted the mix scree

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**solarite_guy** · 10-12-2018, 08:11 PM

Adjust the timing in neutral.

On the box the carb came from, is there a date or date range for the engine application?

What is the manifold vacuum at idle?

Topsy11 · 10-12-2018, 09:03 PM

Quote:

Originally Posted by solarite_guy

Adjust the timing in neutral.

On the box the carb came from, is there a date or date range for the engine application?

What is the manifold vacuum at idle?

No dates on the box. I gave the car details and they supplied. I don't have a vacuum gauge either

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**solarite_guy** · 10-12-2018, 09:55 PM

Ask your mates about borrowing a vacuum gauge. Failing that check online. Good prices are available, BUT before buying anything research both the product and the vendor.