FJ600 Intake Manifolds

I have been chasing a vacuum leak with my '85 FJ600 and discovered an interesting problem with my intake manifolds.

While there are no leaks in the manifolds themselves, they are not sealing to the cylinders. After removing the first one, I discovered that there were minor cracks on the outside of the holes for the mounting screws and that the gaskets were only stuck to the cylinders where the screws are. This was obviously my problem.

What I found surprising was that the sealing surface of the manifold was far from flat and that the brass liners of the screw holes were standing proud of the face. With no reliefs for the tube at the screw locations on the face of the cylinder, these combined to make a very large problem. When I placed the manifold on a surface plate, I was able to slide a 0.035" feeler gage under the edge! New gaskets would certainly not fix this without resurfacing the manifold as well.

 

Yep , you are correct be aware I ordered some new ones gave like 60$ for them and worked great so far on my yellow Seca , I order some for the Johnny Cash bike for 29$ ....they looked fine but were garbage , the vacuum nipple pulled out an all four , tried JB weld ...no luck ...you get what you pay for . When I had my Virago bought some replacement intake boots and they worked great . So you never know , cheers.

 

What about trying some of the thicker gasket paper you can buy worked for me 1.2mm or you can get it thicker the 2mm stuff. On taking mine off and placing them to something flat like glass I noticed they would not sit flat producing some of the vacuum issues you describe, especially hard starting because of air rushing in around the gaps in the rubber to head area. It's a temporary fix but might work.

 

Thanks for the suggestions, but I ordered new manifolds from chacal. Since I plan to keep riding this bike for a long time, I wanted to start with new ones.

So far, I have removed two of the manifolds and both had cracks at the mounting ears that lead me to believe that more cracks are inevitable in locations that would leak to the air passage. The second manifold's brass tubes were not standing proud, but it still rocked substantially on a surface plate, which leads me to believe that the rubber has shrunk due to age. These parts are also only used on the FJ600 and I don't want to need them later and find they are out of production.

 

they should be the same on the xj600, but not many of them over there

 

Chacal shows this to be correct for '84-'91, but they do not show up in the USA Yamaha parts system.

I'll report back when the new ones arrive and I get them installed.

 

The new manifolds from chacal arrived and have been installed. Other than me stupidly destroying one of the gaskets and having to make a replacement from the back of a spiral notebook, the install went smoothly and the vacuum leaks are gone.

 

There are a lot of parts that don't show up, depending on which dealer's ordering system you use.

 

k-moe, I should have been more clear. The USA parts system is very good, but it does not include the XJ600 models sold outside the USA.

So far, I have not had any problems getting parts, especially since chacal has such a large inventory of OEM and reproduced parts. Every single part I have needed (WAY more than I expected going into this project) has been available.