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Honda VFR750 Running Problem

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mjb-is
L Plate Warrior



Joined: 22 Feb 2021
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PostPosted: 11:03 - 22 Feb 2021    Post subject: Honda VFR750 Running Problem Reply with quote

Hi, first post so be gentle.

I have a VFR750F 1991 that I have owned for over 20 years now and I am experiencing some running issues.

Carbs have all been cleaned out and a few refurb jobs done to get through MoT and back usable ready for the summer.

However, the bike seems hard to start and runs 'lumpy'. Choke doesn't seem to help, in fact it hinders starting and seems to start better with no choke and a little turn on the idle adjuster on the left hand side, then backing it back off once warmed up.

After a while it will start to run better as it warms up, but it always used to start easily and on choke normally as you'd expect. It almost sounds like it is running on just 2 or 3 cylinders to start.

I just wondered if anyone has any pointers as I don't have a lot of experience with carbs, usually working on fuel injected cars.

Worst case scenario I will get it into a local bike shop and let them give it a good look over.
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Shaft
World Chat Champion



Joined: 27 Dec 2010
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PostPosted: 11:12 - 22 Feb 2021    Post subject: Re: Honda VFR750 Running Problem Reply with quote

mjb-is wrote:
Hi, first post so be gentle.

I have a VFR750F 1991 that I have owned for over 20 years now and I am experiencing some running issues.

Carbs have all been cleaned out and a few refurb jobs done to get through MoT and back usable ready for the summer.

However, the bike seems hard to start and runs 'lumpy'. Choke doesn't seem to help, in fact it hinders starting and seems to start better with no choke and a little turn on the idle adjuster on the left hand side, then backing it back off once warmed up.

After a while it will start to run better as it warms up, but it always used to start easily and on choke normally as you'd expect. It almost sounds like it is running on just 2 or 3 cylinders to start.

I just wondered if anyone has any pointers as I don't have a lot of experience with carbs, usually working on fuel injected cars.

Worst case scenario I will get it into a local bike shop and let them give it a good look over.


Robby from here would know more (he bought my VFR and resolved the issues) but I had a similar problem and it turned out to be the fuel pump breaking down.

I believe you can rebuild them, but they aren't expensive to replace.
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jaffa90
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PostPosted: 11:26 - 22 Feb 2021    Post subject: Reply with quote

"""but it always used to start easily and on choke normally as you'd expect. """
What did you remove/replace when cleaning the carbs?
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Robby
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Joined: 16 May 2002
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PostPosted: 16:52 - 22 Feb 2021    Post subject: Reply with quote

I had trouble with the needle valves on the VFR. All were a bit sticky, one had failed entirely. You need to also be very careful with any plastic t-pieces and connectors for the fuel line. They will be very brittle by now. I think I replaced most of them with brass.

Mine also had a failing reg/rec - so sometimes when it seemed to be running out of fuel, it was really running out of electricity. Same symptoms. Worth checking the charging system with a multimeter across the battery on a running engine.
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mjb-is
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Joined: 22 Feb 2021
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PostPosted: 17:29 - 22 Feb 2021    Post subject: Reply with quote

jaffa90 wrote:
"""but it always used to start easily and on choke normally as you'd expect. """
What did you remove/replace when cleaning the carbs?

Took caps off and cleaned out float chambers, needle valves and jets. Fitted new gaskets when re-assumbling.
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mjb-is
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PostPosted: 17:31 - 22 Feb 2021    Post subject: Reply with quote

Robby wrote:
I had trouble with the needle valves on the VFR. All were a bit sticky, one had failed entirely. You need to also be very careful with any plastic t-pieces and connectors for the fuel line. They will be very brittle by now. I think I replaced most of them with brass.

Mine also had a failing reg/rec - so sometimes when it seemed to be running out of fuel, it was really running out of electricity. Same symptoms. Worth checking the charging system with a multimeter across the battery on a running engine.

They may have to come apart again then as it's likely to do with the carbs. Probably easiest to take it to someone who can set it all up properly after replacing whatever is required.

The charging system was all sorted recently too by a friend mechanic. Stator and regulators were replaced.
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 18:26 - 22 Feb 2021    Post subject: Reply with quote

Fuel pump points could be getting sketchy by now. The one on my '91 VFR just let go at the end of last year, fitted a facet one instead.

Did you change the sparkplugs while you had it all apart?

If it was running ok before the carbs were serviced and now isn't, you'd have to be suspicious.

If you get a really long screwdriver, you should be able to open the carb drain screws. Make sure they are all filling.

Is the choke mechanism working properly. You haven't trapped a cable or got it back on wrong?

When you look in through the top of the airbox, are all the butterflys resting in the same position and all moving properly when you open the throttle?
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Robby
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PostPosted: 13:01 - 23 Feb 2021    Post subject: Reply with quote

stinkwheel wrote:


If it was running ok before the carbs were serviced and now isn't, you'd have to be suspicious.



This.

Either you had the carbs out, in which case getting them back onto the carb rubbers is tricky. Easy to get an air leak there.

Or you fiddled around and removed bits from the carbs with them in place. Also a very fiddly job where its easy to make a mistake, or to fail to reconnect a vacuum line.
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Old Thread Alert!

The last post was made 3 years, 35 days ago. Instead of replying here, would creating a new thread be more useful?
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