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Thread: Rough hot running

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  1. #1 Rough hot running 
    frequent forum contributor Club Member Blue Marlin's Avatar
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    Hi Guys,

    I have an ongoing issue that niggles at me when out and about. Brum will run better when cold than hot. On cold start up she will be a little rough, bit like myself , but once she gets going she runs great.
    After a while she is just not as sweet running a little rough. Engine water temp is spot on but it is pretty warm under the bonnet, standard for Roadster I guess.
    I have a standard Alfa mechanical fuel pump, which I think is newish as it always looked fresher than the engine. She is running twin Weber 40 DCOE's
    There is also a see through plastic fuel filter on the pump inlet line and this ALWAYS seems just to have a little fuel lying in the bottom corner (it sits at a 45 deg angle).
    She also starts off the button when hot.

    Any suggestions?

    Thanks

    Derek
    Last edited by Blue Marlin; 03-07-2017 at 07:55 PM. Reason: more info added
    Stumbling around in the dark
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  2. #2 Re: Rough hot running 
    Club Member dcunn's Avatar
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    Purely an idea but is the fuel tending to vaporise when at running temp ?

    Check back using the search engine, ISTR several comments on this....or maybe also in Tech Tips ?

    DC
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  3. #3 Re: Rough hot running 
    frequent forum contributor Club Member Blue Marlin's Avatar
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    Quote Originally Posted by dcunn View Post
    Purely an idea but is the fuel tending to vaporise when at running temp ?

    Check back using the search engine, ISTR several comments on this....or maybe also in Tech Tips ?

    DC
    I was wondering that myself. I did some Googling but wasn't too sure as a lot folk also complain of poor hot starting. Found a few suggestions to try after searching here.
    Stumbling around in the dark
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  4. #4 Re: Rough hot running 
    frequent forum contributor Club Member b_caswell's Avatar
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    It could be that when the air under the bonnet gets hot its less dense and the engine will run rich. Try and find away of directing some colder air towards the intakes.
    Ben Caswell probably not the last word on anything here!!
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  5. #5 Re: Rough hot running 
    frequent forum contributor Club Member Blue Marlin's Avatar
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    Quote Originally Posted by b_caswell View Post
    It could be that when the air under the bonnet gets hot its less dense and the engine will run rich. Try and find away of directing some colder air towards the intakes.

    I will try and rig up some trunking and a scoop or fan to direct air onto the air intake and see if that helps. I wonder if an electric fuel pump with regulator might help also?
    Stumbling around in the dark
    Marina based SWB roadster
    Alfa Romeo 1750 with 5 speed box
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  6. #6 Re: Rough hot running 
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    I agree with Ben on this. There's not a great deal of room under a roadster bonnet especially on those with anything other than an A series. Air is less dense as the engine dumps its heat when stationary and the mixture is then richer. Only really a problem with cars equipped with carbs
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  7. #7 Re: Rough hot running 
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    As some at last years Guilisfield will remember I had a similar problem running hot. B engined Roadster. I put 1" spacers under the back edge of the bonnet and a fan to blow cooler air to the carbs and exhaust manifold. Also an SU electric pump. It helped, adjusting the spark timing also helped.
    Am I th only perso t hav problems with missing letters n his for (onthisforum , spacestoo)?
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  8. #8 Re: Rough hot running 
    frequent forum contributor Club Member andyf's Avatar
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    Quote Originally Posted by HairyDave View Post
    As some at last years Guilisfield will remember I had a similar problem running hot. B engined Roadster. I put 1" spacers under the back edge of the bonnet and a fan to blow cooler air to the carbs and exhaust manifold. Also an SU electric pump. It helped, adjusting the spark timing also helped.
    Am I th only perso t hav problems with missing letters n his for (onthisforum , spacestoo)?
    No I e mssd characters aswell
    Mk2 SWB Marina Roadster with a 2.0L Pinto built in 1986
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  9. #9 Re: Rough hot running 
    frequent forum contributor Club Member greyV8pete's Avatar
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    the text suddenly jumps to the line above. Nothing I do will clear it. It is really irritating so I now type all forum stuff into Word and then copy and paste it in.
    Sometimes when I am typing
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  10. #10 Re: Rough hot running 
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    I was getting paranoid, that it was just me. Sometimes I start a forum reply and it gets so bad I dump it. It is not just MOC , I think it is to do with Yahoo. This has just worked perfectly. Light traffic?
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