Mouse Posted June 28, 2019 Share Posted June 28, 2019 Hi I have a 1977 gs750 and a set of gs850 barrels supposedly from a 1979 model. if i use the 850 barrels on the 750 bottem end can i still use the 750 head do i need a 850 one ???. Thank you Mouse. Quote Link to comment
wraith Posted June 28, 2019 Share Posted June 28, 2019 The gs850 has 30/36mm valves and I think the 750 has smaller valves. Also the 850 will have bigger ports being a CV head but then you'd have to sort out carbs for it. The 750 head will increase the compression of the 850 pistons. Quote Link to comment
Mouse Posted June 29, 2019 Author Share Posted June 29, 2019 Sorry for sounding dim but the first part of your post suggests that that the 750 head will not work on 850 barrels, but then you say 18 hours ago, wraith said: The 750 head will increase the compression of the 850 pistons. which sounds like it will work, can you please claify please. Thank you Quote Link to comment
wraith Posted June 29, 2019 Share Posted June 29, 2019 Lol, don't know the size of the 750 valves as my manual dose not give it The short answer is, everyone I know who has done this has used the 850 head. I would think and cannot see why the 750 head would not work on the 850 barrels, but the 750 head being designed for a smaller combustion chamber could give more power but if it has smaller valves that would restrict power (if you can find out what size the valves are that may help) if the 750 has a 36mm inlet and 30mm exh, like the850, I would use the 750 head but if they are smaller and there for restrict the power I'd use the 850 head. The 750 zorst will still fit the 850 (mate used his 750 zorst on a 850 too end) but the 750 slide carbs will not as most of the 850 where cv carbs. Hope this answers your question Quote Link to comment
Mouse Posted June 29, 2019 Author Share Posted June 29, 2019 Hi Thank for the reply, whole lot clearer now i have found out that the 750 inlet valve is . no 27.5mm no info on the exhaust but with this info i now think the 750 head is a non starter. Bit of a arse as now need to look for 850 head an carbs if i go this route. Mouse. Quote Link to comment
inazumarob Posted June 30, 2019 Share Posted June 30, 2019 My local bike breakers ( Plymouth Bike Breakers ) 01752 257763. Has a GS 850 engine in stock, he is pretty cheap on parts normally. Ask for Dave. 1 Quote Link to comment
Mouse Posted July 8, 2019 Author Share Posted July 8, 2019 Cheers for that. Will give them a ring and see what I can sort out Quote Link to comment
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