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Hotter climate, carb and vapor lock issues [message #302671] Sun, 26 June 2016 22:49 Go to previous message
lw8000 is currently offline  lw8000   United States
Messages: 201
Registered: July 2012
Location: S.E. Michigan
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Senior Member
Just got back from a 2 week trip to Orlando from Michigan. We started out in Michigan with temps up to the low 80's. Being in Michigan, we don't see temps in the 80's as often and I had not used our coach much in that kind of weather during the 4 years we've had it. Most of the time we've used it in the 60's & 70's. I made two stops when the temps were close to 85-87, and after getting gas and trying to accelerate to jump back on the highway the engine stuttered briefly but kept going and had no issues while moving. I did notice that while on the highway, the engine's fan would kick in pretty high and loud, and run for about a minute, then spin back down again. This would happen about every 10 minutes or so even on flat road. By the time we got to Orlando, temps were getting upward to 95 or so, heat index touching 100, and I could hear the fan kick in more often and stay running, but at a low hum so it was engaged but slightly. However, when the fan would engage higher and louder, the surging would get worse, and climbing hills I would lose power and when stepping on the gas it would stutter even more. Letting off the gas would let the engine continue running, so I would give it just enough gas to get up the hills then coast down. Finally, the engine quit completely on accelerating from a stop at a toll booth (doh!) and it would not start. From reading in depth on this forum about vapor lock, I was all too familiar with it and figured that was our issue. I removed the wheel wells, let the engine cool for about an hour, then after pumping it several times I saw gas in the carb and it started back up at last. We limped along another 30 miles or so to our destination in Orlando.

We were in the area for about 6 days so I called Jim Bounds to get his help. Fortunately, before we headed home, we were able to get over to him and with his help he was able to narrow down the issue and rule out any fuel system problems by running the gas line from a 6 gallon marine tank to the mechanical fuel pump. We put the marine tank on the floor in the coach and ran the fuel line out the side window, through the front of the grill and down to the pump to avoid it interfering with any moving parts. Sure enough, a few times around the block and still the same surging issues (temps were around mid 80's, earlier in the morning). Jim next put on a known good carb and again I went out around the block, this time no issues whatsoever, this time temps were close to 90. While we were there, he also installed the inline fuel pump that runs from the auxilliary tank hose and switch for us. He also explained that there is a known issue with mostly the 455 but sometimes the 403 where there is a small crack between the two larger rear barrels on the intake manifold. Sure enough, he found a crack starting on our manifold, but it was only about halfway through; if it were all of the way through he said it would be a bigger problem. A huge thanks goes out to Jim Bounds and his guys, they were unbelievably generous at not only working like crazy to figure out this issue, but knew we needed to get home and put us at the top of their list to get this thing figured out. In the end, Jim pulled the carb from his coach and put it on ours, which was a recent rebuild. That, along with the inline fuel pump, got us home. He was also generous enough to let us stay the night using one of his hookups. Several times we were offered a ride to grab lunch and look around the shop while we waited. I just can't thank them enough for all of their help.

On the way home again the temps hit the mid 90's, heat index reaching 100 again, and I think we did experience real vapor lock this time, but only when stopping to get gas. Two times it would start the stutter while trying to accelerate getting back on the highway. Flipping on the aux switch corrected the stutter and restored the power back long enough (takes 4-6 seconds and it just works). Once going for a minute or two, flip the switch back to the main tank and continue on the way. Seems we had a faulty carb as we had surging issues almost 2 years ago when temps were in the 70's and therefore we had ruled out vapor lock. Our local shop had diagnosed that problem to a bad fuel pump and after installing a new fuel pump, we put on over 600 miles without a single issue until this trip. Strange how a carb would work for such a long time then suddenly start to act up, yet continue to work again. We had the original carb and did not know its entire history from the previous owner.

Hope this may help somebody someday, having similar issues. The marine tank idea is a great one as it can quickly tell if there is a true fuel issue, or if it's something else. In our case, the hotter temps (high 80's to low 90's) affected both our carb and I think also caused vapor lock, two separate but very similar symptoms. We are also sold on the inline fuel pump, we have now seen it in action. Also learned about the intake manifold crack that seems to also be a common issue.

Chris S. - 77 Kingsley, 3.70 FD, mostly OEM - S.E. Michigan

[Updated on: Mon, 27 June 2016 11:17]

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