Newer PHM40's with white floats.

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chas b
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Newer PHM40's with white floats.

Post by chas b » Mon Jul 22, 2019 1:27 pm

Hi all. My MHR has replacement carbs on it which differ from the original 40's. Obvious external difference is the black plastic tops but what is bothering me is the white plastic floats that are fitted. This type is not designed to be height adjustable. I also noticed that they are a different weight to the originals. I'm wondering if this has anything to do with the bikes poor starting/running. There must be many bevels that have had their original carbs replaced due to wear so I'm hoping that someone has been down this route.

Lumpy
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Re: Newer PHM40's with white floats.

Post by Lumpy » Tue Jul 23, 2019 4:32 am

Your a little short on info regarding poor running. Someone once said to me that most carb problems start in the ignition. That is, carbs are often blamed for ignition issues. Have you checked carb balance? Comprehensive run down here: viewtopic.php?f=26&t=10

Simple test for main jet/needle position is a spirited run down a lonely straight stretch of road. Constant throttle position for a few miles then abruptly shut the engine down and check plug colour. Correct jetting should show nice tan coloured plugs with a little darker on the outside. Check both plugs.

Manifold gaskets are another cause of issues. The original rubber manifolds deteriorate and allow them to suck air. Very common fault.

Bosch ignition is prone to rotting the insulation on the wires from the ignition pickups. If this wire has not been replaced you would be well advised to do so.

Difficult starting can be poor spark plugs, incorrect plug gap or manifold gasket issues mentioned above.

Put down a few more details if you can because there are some pretty clever bevel heads on this site that will point you the right direction.

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BevHevSteve
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Re: Newer PHM40's with white floats.

Post by BevHevSteve » Thu Jul 25, 2019 11:43 am

You are incorrect regarding float adjustment..... These floats ARE adjustable, I do so literally all the time when I am rebuilding dellorto carbs for customers.

The little 2 fingered hook that holds the float needle valve is what you bend to affect an adjustment.

As already mentioned, you have other issues to deal with, most likely improperly sync'd carbs, valves out of adjustment, bad intake manifold insulators..... The single most glaring issue if you have not already corrected it anyways, is that literally every single bosch ignition equipped bevel drive twin must get the pickup wires replaced with FEP or similar sheathing wires. Luckily we have a kit for doing so available..

https://store.bevelheaven.com/Electrica ... h-MHR-etc/

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https://store.bevelheaven.com/Electrica ... h-MHR-etc/
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chas b
Mariana
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Re: Newer PHM40's with white floats.

Post by chas b » Fri Jul 26, 2019 12:37 pm

Hi Steve, re. the float height adjustment I read it on the Dellorto site. So what to set the height to bearing in mind that the white floats are a different weight... or am I overthinking this?

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BevHevSteve
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Re: Newer PHM40's with white floats.

Post by BevHevSteve » Sat Aug 03, 2019 12:50 pm

overthinking....... `-*

just install and check the normal method and you most likely will find them to be within spec. I rarely need to actually need to change it.
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Steve Allen (925)798-BEVL[2385] Ride'm, Don't Hide'm
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