Carb issues - 1984 V45

[Irisheagle]

Hey guys,

Recently a neighbor was helping me pull the carbs off of my bike so I could rejet due to suspected clogged pilot jets. For the last few months the bike had issues starting but ran great afterwards. While pulling/rejetting/reinstalling the carbs, we've run into some issues that we're trying to make heads and tales of, so I'll give a full rundown of what we did and what the current symptoms are.

Removing the carbs was more or less uneventful. We played it by ear for the most part, including loosening some of the screws holding the carbs onto the vacuum chamber. First mistake. After putting some elbow grease into removing the carbs off the bike, the carb that had been loosened from the vacuum chamber suffered a broken piece. Specifically, it's a little plastic tube approximately 4" long that supplies fuel to it's respective carb. It broke at the very end that seats into the carb. We JB welded it back together and put a new O ring on, put it back into place, and reinstalled the carb back onto the vacuum chamber.

Rejetting was uneventuful. Changed pilot jets from stock 38's to 40's and main jets from stock 95's to 100's. Installed new float needles as well. Used carb cleaner in all crevices, air dried with compressed air.

Putting the carb back - had some signficant trouble getting the carb seated in the boots connecting to the engine. We're still not completey sure we got the top-port carb completely seated in its respective boot, but we believe we did. Tightened down all clamps.


Running the bike
Fed in fuel to the carb, left the vacuum chamber uncovered and started the bike up. Note that there is a definite fuel leak from the top-port carb where the "fuel feeding tube" is located. Have to pull the carbs again to be sure, but looks like the "fuel feeding tube" isn't seated properly, or the repair didn't work. Note: Fuel only leaks when we initially feed fuel into the carbs, and only some leaks. Leaking stops completely while the bike is running.

Initially it starts up like a pro for the first 1-2 minutes, crisp and powerful response to throttle inputs. After 2-3 minutes, bike is giving delayed and muddy response to throttle inputs. Idle RPM drops to below 1k. Approximately 500 ms delay from throttle inputs to engine response.


That's more or less everything I can think of from start to finish. My first question concerns the fuel leak; where is the best place to get that specific part? It's the 4" plastic tube that runs from one carb to another to deliver fuel.

Second question; What would cause the bike to initially have an awesome response for the first few minutes, but then to start seriously bogging down? Is it the leaking tube? Possibly the top-port side carb didn't actually seat into the boot all the way? Having sat for three months with no fuel? The fact that we changed the jet sizes?

Thanks in advance for the help. This is my first time getting into the carbs and I'm sure you guys can offer all sorts of suggestions

Respectfully,
Dave

Edit: After looking a http://www.bikebandit.com/houseofmotorcycles/1984-honda-motorcycle-vf700c-magna/o/m2751, the name of the "tube" we broke is either joint set, C fuel or joint set, D fuel.

[John Luttrell]

You will need to replace that broken fuel tube or risk a fire.  It sounds like the bike is too rich at idle, meaning you went too big on the idle jets; I say this because, the bike can handle the overly rich fuel mixture while cold, because a cold engine requires a little more fuel.  After the engine warms up the rich mixture becomes too much and will cause it to become sluggish off idle and more than likely the exhaust will smell rich on it too.

[Irisheagle]

Yeah, the plan is to pull the carbs again and double check the location of the leak to make sure I get the absolute right part.

As far as jets go; I could try getting replacements for the stock, or try to go the enriched route. Looking at http://www.jetsrus.com/a_jet_kit_street/honda_700_VF700C_magna.htm, it looks like while 40 is the next step above 38, I could try a 98 on the main, or take it back down to stock 95. Suggestions?

[John Luttrell]

I wouldn't think you went too big on the mains, but I'd go back to stock size on the idle jets. 

[Irisheagle]

I'll try that and get post back in a few weeks with the results...

One last question; are there any tricks to getting the carbs off/back on? We opted to leave the radiator on contrary to the Cyclmer book, and it was definitely a huge pain in the butt. I found taking some of the boots off the engine helped some.

[filstoy]

When I removed my carbs I used this write up as a guide. It was still a major pain in the rear but my son and I had them off in a short while.
http://www.bikebreed.com/Honda-magna-&-sabre-info.html#carb_rr

[dgc67]

If you are going with a K&N filter then go with the 40 pilots and 98 mains.

[John Luttrell]

After a little thought on this; after the bike is warmed up and acting sluggish, have you tried a little choke to see if that clears it up?  If applying the choke clears it up, it's too lean still and you probably still have some trash partially clogging one or more of the idle jets.  If applying a little choke makes it act more sluggish, it's too rich.

[Irisheagle]

DG; I do have a K&N filter, although when we were testing the carb (after jetting), everything above the vacuum chamber was off the bike, including the air filter. I'm thinking about dropping the pilots back to stock 38's and the main's down to 98 (one step above stock 95) like you mentioned.

John; When we were initially starting the bike, we had the choke full on. We tried starting it with choke off and it ran fine initially as well. Regardless of choke position, after the bike warms up it starts to bog down. As far as clogged pilot jets; all the jets (pilot and main) are brand new. It's possible the path from the pilot jet is clogged; could try going after it with more carb cleaner and compressed air.

I forgot to mention; when we were testing the bike, we didn't mess too much with the throttle; maybe revved it up to 4-5k rpm in neutral. I figure I'll go back later this week to the place I have the bike at to inspect the carb for the broken piece, as well to mess around with various configurations to see if I can get more specific information on when the bike is bogging down.

[John Luttrell]

DG; I do have a K&N filter, although when we were testing the carb (after jetting), everything above the vacuum chamber was off the bike, including the air filter.

These bikes are very sensitive to the air box being installed to run correctly.  You may want to install the air box and see if the sluggishness goes away.

[Irisheagle]

One other thing I forgot to mention;

I was glancing through the Hayne's manual today and read in the specifications that the pilot jets should be twisted 2 1/2 turns out. I didn't know that when I was rejetting, and thus all four pilot jets are cranked down all the way. I don't know if that would cause the bogging issue, but it's worth mentioning.

At any rate, this weekend I'll start working on running through all the suggestions you guys have given me. Thanks again for all the help

[John Luttrell]

The 2 1/2 turns out, they are referring to is the mixture adjustment screws, not the jets them selves.  The factory setting for the mixture screws is 2 1/2 turns out from gently seated.