D90 2.5l Petrol hard to start with warm engine. - Defender Source
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Old March 31st, 2015, 07:05 PM
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D90 2.5l Petrol hard to start with warm engine.

Rebuilt the carb, new plugs, wires, etc. Dynamic timing set at 16 degrees @ 2000 RPM. Idle air screw is about 3 turns, it won't idle properly with anything less. That's actually how it was before the rebuild. Idle set at 750 RPM (I have A/C). Runs great, but after driving if it sits a short time while everything is still warm, it's hard to start regardless of pumping the pedal or trying to use the choke a little. Float levels set to specs. It starts fine when cold using the choke.


I'm wondering if the following occurs:
  • Would the fuel bowl drain back into the tank like a siphon??
  • Haven't replaced the coil, battery is fine..over 12v before cranking, I haven't checked it when running with the alternator output.
  • I haven't replaced the underbody fuel filter....this weekend
Any suggestions?


Next time I'll try to turn the key on for a while and let the fuel pump run a bit before starting to see if that helps.
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  #2  
Old March 31st, 2015, 07:29 PM
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Not familiar with the carb but is the idle mixture set right? Sounds rich. Normally you close in the idle jet idle it just starts to drop the idle.
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Old April 1st, 2015, 12:02 AM
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I set the mixture per manual. Timed it first, 2 turns out and it wouldn't run. Went to 2.5 turns, set the idle screw to 750 rpm, adjusted mixture until no change in rpm, readjusted idle screw, etc.
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  #4  
Old April 1st, 2015, 08:18 AM
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Quote:
Originally Posted by 89Defender90 View Post
I set the mixture per manual. Timed it first, 2 turns out and it wouldn't run. Went to 2.5 turns, set the idle screw to 750 rpm, adjusted mixture until no change in rpm, readjusted idle screw, etc.
And you did this when fully warmed up?
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Old April 1st, 2015, 08:28 AM
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Yes it was warm, , if you start with section 19 page 3-7, I did it exactly as outlined in the workshop manual. I did set the RPM to 750 because of the A/c.


  • Dissasemble
  • inspection/clean
  • reassembly
  • throttle cable adjustment
  • mixture control
  • fast idle adjustment
  • idle adjustment
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  #6  
Old April 1st, 2015, 09:16 AM
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IMO, you should you back and forth on the idle and mixture settings, not just the once as shown in the manual.. On the mixture, screw out until max rpm is reach and then screw in until it just starts to drop the rpm. It is important to have the engine as hot as it gets, so after a good run on a hot day is the best. I would also set it all up at 600 to 700 as shown and then lastly up the idle if desired.

Have you checked static timing and timing at idle, with no vacuum advance as well? You say you check dynamic at 2000 rpm, but if there is a problem with the distributor advance, your base timing could be off.
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Old April 1st, 2015, 09:20 AM
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I would check to ensure the choke lever is engaging/disengaging all the way and that the mechanism is moving properly.

If the engine was being choked when warm it may be flooding the engine making starting very difficult.
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Old April 1st, 2015, 11:35 AM
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New choke cable, working properly and adjusted properly. I don't choke it when the engine is hot to restart. This was occurring after sitting maybe 30 minutes or so and trying to restart. Ran several errands and I turned the key on for a few seconds before cranking, sort of allowing the fuel pump to prime the carb. Started every time. Maybe blocked fuel filter or may need a new pump. I'll change the filter and see what happens. Anybody know what PSI the fuel pump should be putting out? I'll hook a guage. It almost seems as though the fuel may be siphoning back out of the bowl. I'm going to drive it, turn it off and remove the carb to inspect the fuel level to see for sure.


Static timing is just a few degrees. By dynamic, I set it with a digital gun, vacuum disconnected, engine warm at 2000rpm. Set to 16 degrees. It does have the electronic upgrade in the distributor, so no points.


Specs say 800 rpm with A/c, so that when the compressor kicks in, it doesn't bog down and die. I went through the mixture setting procedure 5 times and always ended up at the same settings.
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Old April 1st, 2015, 12:25 PM
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Coil is always a suspect in cases like this.
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Old April 1st, 2015, 01:13 PM
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If it always starts fine after letting the pump run, then you have the problem there. The carb is draining out. The pump should have a check valve somewhere to prevent back drainage.
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Old April 1st, 2015, 01:26 PM
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Just a suggestion check your fuel line routing. If it's doing when it's hot it may be vapor lock. I've also seen coils work fine in a cold engine then break down when hot.
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Old April 1st, 2015, 02:45 PM
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Check #1
When the engine is cold, disconnect the fuel line and let the line feeding the carb empty into comething like a coffee can.
Is it flowing or dribbling?
When the engine is warm and hard to start, disconnect the fuel line and let the line feeding the carb empty into comething like a coffee can.
Is it flowing or dribbling?

Check #2
A warn engine with low compression will often have enough compression to start when cold.
When warm, the compression will drastically drop.

Take a compression reading on each cylinder when cold.
Take a compression reading on each cylinder when warm.
If the compression is lower when warm, pour 1/2 oz of oil into each cylinder through the spark plug hole, and take the compression readings again.

Report back all test findings to this thread.
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Old April 1st, 2015, 07:55 PM
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I have a 2.25 with the same issue. I have replaced everything and still has the issue. The motor was re-built at some time, before me, and compression is good. If you tun it off and then re-start no problem. However if you wait five minutes it is hard to start but eventually starts. I think it is a vapor lock in my case.
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Old April 1st, 2015, 08:26 PM
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Bruce, I don't think it's vapor lock. I read that the return fuel line prevents that. All hoses in stock position.


I checked the battery voltage today and it was 12.4v. Running the alternator had an output of 14.06v. I do notice that while I'm driving the voltage needle will drop to the lower red on the guage. Don't know if the gauge works properly though. I'm going to wire another voltage guage to the battery and see what's going on.


If I leave the key in the on position for 10-15 sec before a warm start it works fine. I'm thinking the check valve idea and back siphoning is the culprit. The only thing that doesn't make sense about the back siphoning is that the overflow is open to air, which means that the gap above the floats is open to air and the lowest point for the fuel coming in would be the bottom of the float needle housing, which is above the floats and open to air, so even if the line siphons back, the carb should still be full. Doesn't seem possible that fuel out of the bowl could back siphon. I'm going to take the pump out of the tank and have a look, maybe some trash??


Maybe the key being on "energizes" the coil and that's why it works if I leave the key on for a little. I'm going to replace the coil and see if that helps.
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Old April 1st, 2015, 08:56 PM
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Quote:
Originally Posted by 89Defender90 View Post
Bruce, I don't think it's vapor lock...
A siphon-off scenario as you describe is null and void with an electric fuel pump that delivers the required amount of fuel.
Drain back and drain off are completely moot when fuel is pumped in a steady stream and NEVER were a consideration at solihull.
Your issue is related to something else if in fact you have adequate fuel delivery (something yet to be confirmed, see post 12) .

Assuming the carb was rebuilt to working specs, the compression and fuel delivery is in the critical starting path as asked about in post #12.

Once we have established the amswers to post 12, we will move on to the coil, sparking plugs, high tension leads and so on...

Have you conducted the test in post 12 yet?
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Old April 1st, 2015, 09:10 PM
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He already stated that if he runs the fuel pump for a few seconds it will start right away. It only won't start if he does not let the pump run for a few seconds.
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Old April 1st, 2015, 09:38 PM
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Yeah, what Red said...
I'll get to #12 this weekend, but for argument sake...

  • There's obviously fuel in the carb when I turn it off, why wouldn't it be there when I try to restart if the siphon effect is null? I do come to a complete stop, pull up the brake, try to remember to turn the key the other way as to not grind the starter. So it gets a chance to idle for a bit, and it's smooth.
  • If I turn the key on for a few seconds before starting there aren't any issues, I want to think that it's the fuel pump, but then again, there's already fuel in the bowl because the siphon effect is null. So now I'm thinking electrical right?
If there's fuel in the carb because the siphon effect is null, why would I do check #1?
If I leave the key on for a few seconds before starting and the issue does not exist, does that mean the key being on fixed my compression problem you're referring to in check #2?
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Old April 2nd, 2015, 12:17 PM
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There is an anti-siphon solenoid valve built into the 90/110 four cylinder carb setup as part of the Weber 32/34 dealy-o.

Too bad Charlie, the Braniac Confucianist from Clarksville, TN has everyone blocked so he can't get the answer to his question.
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Old April 2nd, 2015, 07:49 PM
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Quote:
Originally Posted by 89Defender90 View Post
Yeah, what Red said...
I'll get to #12 this weekend, but for argument sake...

  • There's obviously fuel in the carb when I turn it off, why wouldn't it be there when I try to restart if the siphon effect is null? I do come to a complete stop, pull up the brake, try to remember to turn the key the other way as to not grind the starter. So it gets a chance to idle for a bit, and it's smooth.
  • If I turn the key on for a few seconds before starting there aren't any issues, I want to think that it's the fuel pump, but then again, there's already fuel in the bowl because the siphon effect is null. So now I'm thinking electrical right?
With bleed down, if there's fuel in the carb because the siphon effect is null, why would I do check #1?
If I leave the key on for a few seconds before starting and the issue does not exist, does that mean the key being on fixed my compression problem you're referring to in check #2?
The siphon effect doesn't matter (I used the term null and void) because the float chamber of the carb should stay full of fuel.
To check you can unscrew the top half of the carb and visually inspect the fuel chamber.

Even with bleed down, if your fuel pump is pumping enough fuel, it will refill the fuel line with gasoline quickly enough that the engine should start on the residual fuel in the float chamber and a second or 2 later have fuel refilling the float chamber as the engine uses gas.
The reason for checking your fuel pump is to be sure it is delivering enough fuel.
For example: I have worked on weber carbs that had a bad needle and seat or a mis-adjusted float level that were adjusted to run fine, but suffered from a low float level that were hard to start.
The only noticeable effect once started was at highway speeds the engine would reach a point where it starts loosing RPMs.
If your float chamber is low and or your fuel pump is not producing enough fuel and leaves the float chamber low, then the engine will be hard to start.
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UD: "Just Power through it man!"
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  #20  
Old May 13th, 2015, 02:49 PM
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Read this post a while back and was kinda curious what others input was since I was having the same problem with the 2.25 petrol in my 90 . I only recently got the truck out and have been preparing for the MOT. While underneath it yesterday, with the engine running I noticed a drip in the area of the fuel tank. I discovered it came from the electric fuel pump. First I assumed it was just the fuel line not being fitted tightly, but it turned out to be the brass fitting on the outlet side of the fuel pump. It would weep gas past the threads as the truck was running. I pulled the fitting and added a bit of teflon tape, snugged it up and re installed the fuel line. Fires right up now regardless of sitting, warm or cold. This was obviously an air leak once shut off causing the bad start issues.

Not sure if this helps but figured since having a similar issue I would mention it. I also noticed that the fuel pump is much, much quieter before starting as it was quite noticeable before. I guess because it now does not lose it's prime as it did before. Hope you have some luck sorting out your issue.
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